I am GNU/Linux only - but the problem seems to have existed in the past - as for Linux it is said to be 32 bit
only and thus it would no longer run on macOS 10.15 `Catalina' and above - and in this situation GOG typically
no longer shows the Mac symbol on the product page - while the old mac version is still there.
But the 32 bit info is old an outdated.
I just checked and the 1st part has the same version on Mac as on Linux on offline installer - were it is a 64 bit version.
So it is available and will most likely be 64 bit and thus work fine.
I will contact the Devs - maybe they can change the wrong info on GOG - the 32 bit problem seems to not
be correct - while I reported it concerning a refund for Iron Marines to GOG support - which lacks the Linux version
(while on Steam it seems to exist).
I will report info from Devs (if I will get some) on this thread:
and after having created this thread I saw your question - which is related to the current mess.
But it's not the Devs - as the looked for quality of life for their games and do care.
I hope this helps - even though I can not guarantee anything - as I don't use Apple HW. ;)