I use an app called Seal. You could think of it as a fronted for youtubedl. The interface is really beautiful and you can download videos from many different websites.
Another one is ViMusic, this is just an app that streams songs from YouTube music without any ads.
edit: fixed spelling of vimusic
TrackerControl is an Android app that allows users to monitor and control the widespread, ongoing, hidden data collection in mobile apps about user behaviour (‘tracking’).
Not sure if it's only on F-droid, but I've switched from G-board to Open-board. It's a virtual keyboard app that has many "extra" features compared to Simple board. There's autocorrect, swipe to complete, and a clipboard visualizer. I'm trying to figure out if I can add entries to the dictionary so it suggests some words I use often instead of others tho.
Many apps that are on F-Droid are also on Google Play, but there are exceptions. Gadgetbridge (smart watch connection app) warns that the Google Play version is unofficial and unaffiliated. An unofficial app might be upstream compiled without modifications, but this opens users to potential supply chain attacks from the uploader and Google.
Tachiyomi, but honestly I mostly use Neko which is a fork of TachiyomiJ2K which is a fork of Tachiyomi. Both aren't on Fdroid but at least they are completely FOSS.
It's the best Manga reader out there and it supports basically every Manga website out there and more.