If you don't need anything except typing, Simple Keyboard might be what you're looking for.

I've experienced the same on GrapheneOS and haven't found a solution. :(

I had to look it up. It's the community image (apache version) from https://hub.docker.com/_/nextcloud/ which I use together with a mariadb and redis image.

Mine runs very smoothly. I set it up on a Raspberry Pi 4 (4GB) with an external 1TB drive. I run it in docker with the official (?) image and can't remember having set any special config. If you have any questions, I'm happy to answer them. :)