Hi, this is so annoying, I have the same problem, but never received reply here. I want to work with physical keyboard and use on scren one at the same time, but it is impossible with new android 15 or 16.
This works fine with android 11 on my old samsung S5 ( /e/OS), where the setting is still present. Graphene does not have the option to disaplay on screen keyboard, but I think it is google's problem, not graphene's. Google behaves like apple, they think when you have physical keyboard, you don't need to have a virtual, so they don't let you display it. This is problem with barcode reader for me, which emulates keyboard, but does not have other keys.