I've not used it, but there's an app and OSS+commercial code for custom keyboards: https://keyboardkit.com/app https://keyboardkit.com/app and https://github.co

I've not used it, but there's an app and OSS+commercial code for custom keyboards: https://keyboardkit.com/app https://keyboardkit.com/app and https://github.com/KeyboardKit/KeyboardKit https://github.com/KeyboardKit/KeyboardKit