Been using a degoogled LineageOS phone with all apps being exclusively FLOSS. My favourite free alternatives to proprietary apps and services must be Lemmy (Jerboa) for Reddit, ArcaneChat and Matrix (Extera) for Telegram, Fluxer for Discord.
Which ones are your favourite?
I didn’t say everything from your post was new to me. Fossify I do know and their apps look pretty decent although somewhat barebone. I usually need more features so I ended up using other FOSS apps.
If you want a more advanced file manager, try Material Files. They’ve been revived now. If not, then maybe Amaze File Manager. If you really wanna go crazy, WM Keyboard has a built-in file manager aswell