Here's another question about this process. In BIAB 2019 for Mac, you can't record your user track in BIAB itself; only the Windows version allows this. (It seems the Mac version is somewhat "behind" the Windows version. The 2019 doesn't have the Style Maker option, either.

Question: does the Mac version 2021 allow recording in BIAB?

BTW, the reason I'm even doing this is that the RealTrack bluegrass guitar does not sound like Bluegrass; it's just strumming. Bluegrass rhythm guitar is played bass-strum, bass-strum, alternating root,fifth bass with a back-and-forth strum, sometimes connecting chords with walkups, walkdowns, an occasion "Flatt" run, etc. You can hear that on the .wav file I sent.
Cheers,
Alan