Ergopad is a tool for creating custom keyboard layout.
It's not ready yet! But if you feeling curious you can try it on https://pashutk.ru/ergopad/, you'll need a device with a touchscreen (mouse will work too but from a practical point of view it's pretty useless).
Open an app, place your hand over screen and start tapping the screen with your middle finger. Don't move you wrist, only fingers and try to tap on the screen several times like if you were pressing keys on bottom, home and top row of a keyboard. After that select another finger at the topbar and repeat it for every column. You've got your personal layout!
Exporting the resulting layout is not available yet, but we'll get there.