I appreciate your response, Howard, but I think this cannot be where it is stored. I found this in the registry, too, but none of these values (mine match yours) change when the GFXDX12 command is used to change the value. This registry key seems to be storing some sort of "default" for the application (perhaps on first launch and/or after a reset?) as well as some other "parameters" regarding the variable.
It seems there must be some other place where the current setting is stored for each profile (or at least for some of them).
When I do a registry search for "GFXDX12", I find one other instance, beneath a particular AutoCAD "profile" name that I know was current when I executed the GFXDX12 command and changed the variable from 1 (default) to 0 (zero). There, it does show the value as 0.
Yet, there are other AutoCAD 2024 profiles (the "unnamed" one and others I created) in the registry under which "GFXDX12" does not appear at all.
So, based on that, what seems to be happening is that for each profile, the setting "defaults" to 1 unless the GFXDX12 command is used to change it to 0. Then, the key is added to the registry under the current profile (as a way to "override" the default setting, I assume).
However, if I execute the GFXDX12 command again to change the variable from 0 to 1 and then close and re-start AutoCAD, the value of that registry key does not change to 1 (or get removed from the registry).
It's confounding!