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?
There is HeliBoard, but swipe typing unfortunately requires Google’s gesture typing library at the moment. There is work being done to create a foss replacement for the gesture typing library.
Not yet usable for a pure foss system, but it will be once the gesture library is ready.
I replaced FUTO with HeliBoard quite a while back. I’m contributing swipe data to help the effort with an open swipe library.
Overall the only feature I’m missing is changing to COLMAK.
There is a system in place (and accessible) to use custom layouts iirc.