What instructions or guides do you recommend?

The project linked is a fork of the version on F-Driod. You can download the APK directly from the Github and use it just fine.

Thanks for the additional reading and information. Maybe it’s just me, but I feel like I hear about a security vulnerability in “processor microcode” or packages or other software basically every day. As a relatively non-technical user, it’s always very difficult to tell how much these things actually matter for normal users. Flatpaks are incredibly convenient because they “just work” and are easily compatible with immutable distributions. For better or worse, I suspect many people are not going to be dissuaded from using them by hypothetical/abstract security risks.

Can you say more or provide a source on why you shouldn’t use a browser as a Flatpak? Is it just because the sandboxing is potentially weaker?

Any tips on how to actually learn this keyboard? Do I just force myself to use it as much as possible until the movements start to become muscle memory? How long might that take?

It will probably get made eventually, but they have said there is no ETA for now. In the meantime, you can upvote the suggestion on their feedback forums.