Is there a way to get recommendations for "underrated" songs, or music that is awesome but I might not come across? For instance, I really loved the Peacemaker soundtrack...

I fucking hate YouTube Music, but the discovery algorithm is undeniable brilliant, even compared to Spotify
It takes maybe six months of skipping tracks you don't like and fully listening to ones you do to teach it, but after that it's pretty amazing
I share an account with my wife who has a hugely different taste, but it manages to find stuff we both like
ReVanced is the way
- It takes maybe six months of skipping tracks
  Lol, I look forward to good results by the end of the year? Maybe not the best algorithm after all.
  I personally don't have one particular way of discovering new music. It's a mix of suggestions from different apps or friends. Shazam during movies and TV also helps guide some discoveries. Also just clicking through a rabbit hole of suggestions and marking stuff you like for future digging.
  
  The algorithm will figure your rough taste out in a day.
  But like most things in life, you'll find patience does amazing things
- If you do find artists you like on Youtube (as in people who actually run their own channels) they might collaborate with other interesting artists too on some songs. That is a great way to find new artists.
  
  Yep my wife loved the french band Deluxe's "Flowers", amazing track right enough
  The algorithm started suggesting stuff by a guy called Chinese Man, very odd, not our usual stuff but strangely likeable
  Turns out he's the producer for Deluxe. Listened to a couple of his tracks that are kind electronica, the algo suggests more electronica which we skipped most of, the algo figures out what style we liked in that niche (to us) category.
  And that's just one example, I've discovered hundreds of bands because of it
  As bad as Enshittification is, some bits of it are incredible
- Really? It's way worse than spotify for me. It pretty much plays the same set of songs whenever it autoplays no matter what it's trying to base the autoplay on.
- Do you use ReVanced with the default Play Music app? What are the advantages?

Completely ignoring your question to say, that Peacemaker soundtrack is awesome! I had no idea about a lot of those songs but now the title track is my ringtone. Lol
- James Gunn generally does a good job at choosing music for his movies/series
  
  Yup! GOTG soundtracks are really good!

Many, perhaps most, music services have towards the bottom of an artist page a list of similar artists that you can explore. Also, if you see what compilations a song, or an artist, is on you can see what else is on that collection.
Also, music services have collections for different styles of music. As you listen to those, if you like a song you can try to see if you like other songs from the same group / artist.

Local community radio show. CKUT and CISM in Montreal have great niche music shows: math-rock, electronica, experimental, underground hip-hop, name it, there's a show for it.

Whenever I find a new artist I like I’ll make a pandora station based on one of their songs. It usually reveals a bunch of similar artists, it’s how I found Noah Kahan around pandemic time

BBC Radio 6 Music has a lot of obscure stuff, especially the DJs like Iggy Pop and Craig Charles.
Edit: also, go to a local open mic night, find someone whose music you like, and make friends with them. They'll have loads of obscure recommendations for you.

You could try random internet radios, usually long lists are easily searchable and just listen to them for a few mins at a time to see if you like anything then if you do look up that bands albums, or if you're really interested read up about artists and what music inspires them and branch out from there.

I hate to say it but Pandora has been useful here, when it actually finds similar sounding bands rather than just bands from the same era.
I found Tape Five by spinning out from Postmodern Jukebox, for one example.
- I love Pandora, specifically for the "radio" feature where you create a station based on a song or artist. You can even add diversity and throw in another artist or song, and it blends your choices together to make predictions. Then you thumb up and thumb down, and before you know it, every song is up your alley. I gave up Spotify years ago bc the radio function sucks and give Pandora my money instead
  
  I just don't like to advertise. If I can promote a solution that doesn't advance a particular oligarchy, that's my preference.
  But when the tool works, I admit it.

I’m lucky to live in a really good radio town. For the last 10 years, I have found the best new music consistently from the KUTX community supported radio station.
You can listen to them online too. Laurie Gallardo is sort of my low key hero.
https://kutx.org/

Are you in the US? You might want to check out the eurovision song contest. I've become familiar with a lot more new music that way.
- If you like that, check out San Remo -- unlike the EVSC, it's less about politics and more about talent, and Italians really know how to get experimental

The last few times I've found music I like via a method that was repeatable was searching through tags on Bandcamp. If I was listening to something I liked, I could look at the tags (electro, downtempo, big band etc) and click a few of those to find similar music. As far as a filter for quality, the number of followers for a page might be a decent metric because the genres are extremely precise and niche, and most of the biggest artists don't self publish. There's some amazing stuff on there to be found.

I use Pandora a lot. Often I'll go to YouTube to watch the video.
So I put in a station on Pandora and when I hear a song I really like (or several I like from one artist) I put that artist in as a station on Pandora. Lather, rinse, repeat. I'll usually find a bunch of new stuff I haven't heard before and I'm pretty sure many of them are from little known artists because when I put their songs into YouTube, I notice they frequently have few views. Ex. Jem. Hope this isn't too obvious.

I like finding playlists that people on Spotify have made roughly around a particular band or genre. I find one and hit shuffle and see what happens. I'm talking an actual user made playlist, not the garbage Spotify "made for you" playlists. Those used to be solid until they started stuffing them with 90% songs I already listen to.
Sometimes playing the last song on an album that I like or one of my playlists gets some good stuff out of Spotify's algorithm, but that is kind of hit or miss. It used to be quite a bit better.

Get some friends that like the same “kinds” of music as you. Ask them.

And You Will Know Us By The Trail of Dead’s album So Divided! https://music.youtube.com/playlist?list=OLAK5uy_kxLqnOo6nF_rB-JCbX2yf_AfsfPDx5h3k&si=CweERMj0J0MOpXh8

I’m hesitant to link back to reddit, but I’m not sure there’s any community with quite the same amount of engagement/content yet. They have rules against number of views/plays to try to keep posts about lesser known stuff.
https://www.reddit.com/r/listentothis/
The few things I liked about siriusXM when I had a subscription were alt nation (except Madison… ugh) and XMU. The DJs occasionally had insight into their choices but you can find the playlists themselves here
https://xmplaylist.com/station/siriusxmu https://xmplaylist.com/station/altnation

Pop Songs Your New Boyfriend's too Stupid to Know About https://www.mixcloud.com/PopSongsMixtape/

"Underrated" and "awesome" tend to just... mean roughly the same thing in this context, and it's so individual it's hopeless to try to recommend stuff based on that alone. Popularity or unpopularity doesn't necessarily speak to how much you'll like it, either.
Recommendations are easier to give the better you know your tastes, and the better you can describe them.
You can also do some thinking about what you like and why, and see how others describe that song/album/artist/whatever to get some useful starting points. If you want to nerd out, Wikipedia and the like can tell you a lot about musical influences that shaped this or that style, and you can track it down and see if it resonates with you.
- I'm really talking about quality material I'm not familiar with. I grant that even though it of high quality I may still not like it. But I would like to discover objectively good music that isn't going to be played on the radio, or XM Sirius, or any other common interface.
  So underrated speaks to popularity; underrated material isn't going to be appreciated as much as it deserves. Whether I find that underrated material awesome is my own decision. But if like to have the exposure.