We have clients wishing that versions of Archicad could be compatible with more than only two versions Mac OS.
I'm not quite sure what you mean.
Archicad can only save back one version at a time.
But if you have the previous version, you can open the file in that older version and save back one more version.
You can do that for as many old versions as you have installed.
All the old version can be downloaded.
But be aware you will lose data when back saving - new features do not save backwards.
One of the forum moderators. Versions 6.5 to 25 Dell XPS- i7-6700 @ 3.4Ghz, 16GB ram, GeForce GTX 960 (2GB), Windows 10 Dell Precision 3510 - i7 6820HQ @ 2.70GHz, 16GB RAM, AMD FirePro W5130M, Windows 10