recommendations for desktop Lemmy client?

Same as for every other website: Firefox.
- I really like Photon, that is a web client but with Firefox PWAs addon can be installed a regular app
  EDIT: just seen someone else wrote the same in a different comment, wooops
- Been feeling old and out of touch lately, and seeing this was comforting somehow.
  I mean, I'm still old and out of touch, but it's nice to see that one particular ancient technology might still be considered the best way to do something.
  On the other hand, desktop computers are getting a bit long in the tooth as a concept these days...
  
  Companies pushed for us to install their apps on our phones so they could force ads on us and extract (meta)data from us that they couldn’t from our browsers.
  Cory Doctorow: How lock-in hurts design
  More than half of all web-users have installed ad-blockers.
  This is why services are so horny to drive you to install their app rather using their websites: they are trying to get you to do something that, given your druthers, you would prefer not to do. They want to force you to exit through the gift shop, you want to carve a desire path straight to the parking lot. Apps let them mobilize the law to literally criminalize those desire paths.
  An app is just a web-page wrapped in enough IP to make it a felony to block ads in it (or do anything else that wrestles value back from a company). Apps are web-pages where everything not mandatory is forbidden.
  Seen in this light, an app is a way to wage war on desire paths, to abandon the cooperative model for co-innovation in favor of the adversarial model of user control and extraction.
  And now this corporate brainworm has infected our desktop environments, even Linux ones. Just say no.

It's called a browser? :-)
Honestly, I don't understand people downloading apps to run things like discord, facebook, spotify, and now lemmy. These are webpages, and were designed to work as webpages. So, best would be to use a web browser.
- In my opinion there should be more apps. I hate that they are just webpages tho
  
  I've never heard that take before. Can you explain why you think there should be more apps instead of using the browser?
- For me, it's to have one less apps.

You mean, like ... browser?
No, really 🙃
For Firefox this exists, all other browsers have this functionality directly implemented. Chromium-based browsers can usually be started with parameter --app=https://example.com to start example.com in a SSB/PWA-looking window.
Plus: With this you do not lose the ability to open links in new tabs and you have access to your default configuration for websites.
- Wow that extension is nice! Way better than the overcomplex "Firefox PWAs" I suppose.
  
  Way better than the overcomplex “Firefox PWAs” I suppose.
  Yep. Technically it just creates a new tab that creates a popup with the requested URL and the created tab closes itself after the popup was created. So not really a PWA but just a popup with a website in it, but in most cases this is absolutely fine since you're online anyways, and modern browsers are good with caching.

It’s not exactly desktop, but I use Voyager. It’s a web app. You can also self host it if you don’t want to use the developer instance (I’ve got mine running in docker for desktop use. I use the Voyager app for iOS)
- Thats what im using for android. Its great, but not on desktop
  
  I use it on desktop exclusively, it works well and I like it better than any of the native Lemmy UIs.

Mozilla Firefox

Damn, I was looking to make one of these couple months back but when I asked most people said they were uninterested so I stopped
- Make one, if for nothing else as a portfolio piece!
  
  Maybe. It may have been ambitious for the time. I've been working on simpler projects in the meantime

You should really just use a browser, but I'll at least try to answer the question.
I've never tried any of them myself, as I'd just prefer using the website on desktop, but here's a list of mobile and desktop apps for Lemmy (just look at the right column to see which ones are desktop clients).
It looks like neonmodem is available in the AUR, though it's a CLI utility. If you're looking for a GUI, there's lemoa, but it's currently unmaintained, or lemonade which appears to be pretty minimal.
Your options are pretty sparse, so you're probably best off just using a browser if you're looking for a GUI. I hate to be one of those guys, but you don't need an app for everything; the browser can sometimes provide the best experience.

Photon as a PWA
- Whats PWA?
  
  Progressive Web App

Just use a browser. Or install Waydroid and install Eternity to it.

This project show all different front end/apps/.. : https://github.com/dbeley/awesome-lemmy?tab=readme-ov-file#alternative-front-ends

If you really want an app-like interface, you could make use of Epiphany's "Install as Web App" feature. Just open Epiphany, go to your Lemmy instance, login, and then select "Install as Web App" from the main menu. Like magic, you get a "Lemmy App" that you can bring up like any other app.
This is my experience in GNOME. Presumably though, it'd work with any desktop environment that respects the XDG standards.

I use Ferdium on my desktop and self host my server for it, then just add it through there. Works quite well. Plus, with Ferdium, I can add other services such as Discord, and Mastodon so, it's sort of my go to hub for a lot of my social media.

There's lemoa https://github.com/lemmygtk/lemoa
But I can assure you that it won't be better than the PWA.