The trick here is to inject events as if they came from the user. The virtual-keyboard works really reliably, you can see it over at https://github.com/awwaiid/ghostwriter/blob/main/src/keyboar... . It is the equivalent of plugging in the reMarkable type-folio.

Main limitation is that the reMarkable drawing app is very very minimal, it doesn't let you place text in arbitrary screen locations and is instead sort of a weird overlay text area spanning the entire screen.