I was finally able to upgrade my MacBook Pro to Big Sur, and now I have a script that runs on the latest macOS versions, successfully disabling all the processes that tend to interfere with our stage setup (GigPerformer 4 and QLab). Because I have a non-Apple system drive (an OWC SSD), the Monterey installer refuses to run, so I am stuck with Big Sur. But I’ve tested the script on Monterey in a Parallels 17 virtual machine, and it works just fine. You can find it here: Disable Big Sur and Monterey services · GitHub
I also disable spotlight indexing and automatic software updates, and kill some still-running processes - see the Comments section.