KDE devs have been quietly working on Plasma Keyboard, a new on-screen keyboard for desktop and mobile part of the “We Care About Your Input” KDE Goals initiative. Although not ready for texting yet, it has been making progress. Hopefully it’ll be in a screen near you soon. Join the effort!
https://invent.kde.org/plasma/plasma-keyboard
As long as it has modifier and F keys, accepts mouse input and is manually toggleable I’m happy. Bonus points if I can configure it to show those and number keys per default.