Apparently, TGC recently added some security in the form of Steam Authenticity checking of some kind (from what I've heard). With the current Steam version, you can't even run MAX if Steam is in Offline Mode! My guess is this "feature" got propagated to all versions of MAX, regardless of whether they were Steam versions or not.
Intel i9-10900K 5.10GHz, 64 GB RAM, Nvidia GTX 1080 ti 11GB, Windows 10 64-bit, dual monitor display