We have been making HUMAnN 3.X compatibility releases for successive versions of MetaPhlAn 4. For example, the most recent HUMAnN 3 release (3.8) added compatibility with MetaPhlAn 4’s Oct22 marker/SGB database:
You would need to make sure you’re using a compatible MetaPhlAn 4 and HUMAnN for this to work, as HUMAnN is very careful about not interpretting MetaPhlAn output that it isn’t specifically trained for.