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It's a DosBox game, for f's sake. I've played it on Linux before.

Why on earth is it marked as not compatible?
MacOS has chosen the "smart" decision to cull 32 bit libraries; which means that DOSbox would be left in the rain.
One more thing: GOG also must have the right to sell it for Mac to have a MAc version and without that they will not list it as compatible with Mac.
If you download DOSBox yourself and launch Master of Magic on your Mac (I copied the game directory from a Windows installation) manually, everything works just fine on a recent MacOS (Monterey in my case), regardless of 64-bit.