ArchiCAD and other single threaded apps will not lock themselves onto a single processor (processor affinity). Thus, if you have such an app running at 100% on a single CPU system, it will be about 50% on each of two CPU's and 25% on each of 4 CPU's, typically - and not counting all of the other things running your system - simply because of the way the OS schedules things (time slicing).
If you're seeing 75%, Rick, it means that ArchiCAD is using part of each processor, and other things are using the rest...ArchiCAD isn't using more than the equivalent of 100% of a CPU, unless it is doing a LW rendering in which case it can use all CPUs.
http://www.archicadwiki.com/Multiprocessing
Karl
AC 28 USA and earlier • macOS Sequoia 15.2, MacBook Pro M2 Max 12CPU/30GPU cores, 32GB
One of the forum moderators