Fairemail has been my trusty email client for years. Don't be spooked by its many options, once accounts configured the UI doesnt show unecessary stuff IMO. Some unique and useful features.
But if you want something simpler there's K9, now Thunderbird. Although I still experience the issue with emails not arriving on time with this newer version
KeepassDX, great password manager, good UI, keeps improving.
HordeNG (taken down from Google play, but if was basically just a wrapper for a web app which you can install easily from the browser anyway - https://horde-ng.org)
There's syncthing-fork that I hope will continue to be maintained (especially as they committed a guide on how to switch from the official app 2hrs ago). I've used it already before the depreciation of the official app and it's working reliably.
It looks like Play Store releases are planned to be stopped, so it's probably best to install it either directly from the GitHub releases (for this, Obtanium is also a great tool for finding and updating apps from lotta sources), or with F-Droid.
Grayjay ane newpipe are my go to for youtube. Im starting to prefer grayjay due to the automatic backup and being able to watch twitch, kick, odysee, YouTube and more in one app
Kvaesitso and Heliboard are my most used, since its just the homescreen and keyboard lol. For favorite I'd probably say Pipepipe, been watching a lot of YouTube and I'm sick of ads.
TrackerControl for keeping my phone mostly ad and tracker free
Auxio for music, but I'm considering an alternative, I can't make it ignore certain folders so a lot of received Whatsapp audio shows up on the playlist