For me, Heliboard is the best option. FlorisBoard is cool too if you like their interface, but Heliboard is super customisable. You can change the symbols around, padding, colours, etc., and it supports plenty of languages and can work well with Whisper for TTS, and the auto complete suggestions is quite accurate in my experience. You can also change the toolbar to include copy paste, undo and redo, left/right, etc.

Heliboard also has glide typing, which requires the installation of a proprietary library, which I just tried out and it works really well! There’s also a tab to “train” the glide typing so that the Heliboard team can help develop a fully FOSS library (basically, it gives you words and you glide type. It’s like an opt-in quiz)