I don’t think Firefly has ever implemented processing of the Album Artist tag. Pretty sure it’s been discussed over the years, but don’t think it ever made it into the code. So I don’t think Album Artist ever gets stored in the SQLLite schema (haven’t actually verified).
But it looks like a group is trying to revive development (see posts above)….so perhaps once they get things going, Album Artist support is something we should request as a new feature.