Try disabling SIP. If you’re unable to do that, then you can conclude that you no longer own your machine. Otherwise, it’s merely Apple making macOS effectively less secure by making it unusable with SIP activated.
Disabling SIP also disables your ability to run iOS apps on Apple Silicon :-( It might be for copy protection reasons. iOS apps are partially encrypted and without SIP you could probably access the decrypted version.
It's not a great solution as you need to do a full reboot every time to switch SIP status.
Can also muck with Apple Pay.
You don't have to keep running the same OS on the hardware you've purchased, so SIP isn't a great test. Windows also has protected system files but can still install Linux instead.