Have you tried AnySoft?
Discussion
That's the one I'm using actually!
It's unfortunately the least shitty of all the options.
Have you tried FlorisBoard or the maintained fork of OpenBoard? They are well received among users.
Which one do you like the most?
That OpenBoard fork has more and is maintained more often.
Personally I use the official Google keyboard and disable the internet access with the Network permission, but those two keyboards both are excellent.