I think you will find that Graphisoft have ceased development for AC8.1 as AC9.0 is being heavily marketed and they would prefer/recommend you to upgrade.
That's what happened with previous versions of ArchiCAD the most galling being the "upgrade" from 7.0 to 8.0 for the Mac
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics