Something else is obviously amiss, as with the configuration that you list in your signature, you should see a significant speed-up with 12. But, do note that the increased speed only happens during certain operations, primarily involving 3D generation such as section/elevation generation and 3D window generation.
Are you accessing any files over a network?
Karl
One of the forum moderators
AC 28 USA and earlier • macOS Sonoma 14.7.1, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB