Use APKPure App
Get Soft Keys - More Settings old version APK for Android
Aktywacja klawiszy na ekranie, cieszyć się nim! Nie trzeba zakorzenić.
Activate the on-screen keys, enjoy it! Don't need root.
simple and easy to use version here :
https://play.google.com/store/apps/details?id=com.dogusumit.softkeys2
source codes here :
https://github.com/dogusumit/SoftKeys-MoreSettings
This app uses Accessibility services.