Im preety sure this question has been answered before but i cant find it-
Please read this topic and note the final reply of May 2024:
Make Themes able to be included in .bundle files
The ability to access and modify/create application level files on android has become worse as time goes by.
At the moment, it’s only possible to add a theme by putting the particular theme file into the appropriate resources folder location of the krita application.
There are ways of doing it but they are risky if you’re not very familiar with doing that sort of thing on android.
It’s a very long time since I did application level file prodding and poking on android so I really can’t give further advice about this.