thanks for reaching out (and for the PR lately). Although the app component successfully targets CUBA 7.x, it unfortunately currently only supports the old screen based API.
If you just switch to old API everything should be fine even with CUBA 7.1.
Perhaps you have an idea what would need to be changed in order to make CUBA 7 based API also work? I have not really looked into it, but as you already seem to be somewhat familiar, perhaps you can just give it a try to support both APIs?