You'll need to provide specifics if you want solutions to many of these issues.
- What exactly isn't working with your Yubikey?
- Which bank apps? Did you check the compatibility list maintained by GOS?
- Which apps aren't working without Google Play?
For the keyboard, there are several FOSS keyboards which support spacebar navigation, but you can also install Gboard and simply disallow any permissions, including network access.
Regarding Signal, this would be a reality for anyone with a non-Apple device. You may need to find a compromise and simply use SMS, RCS, or even just email when dealing with certain people.
There will always be one-off features available only on other devices or platforms. Only you can decide whether they are worth the cost of security and privacy.
As mentioned elsewhere, the easiest method is to encrypt only the data drives. This way you can secure shell into the server upon restart and decrypt the data. I've been using this method for years now without issue.