I would say this is 75% correct.
1. Most of the software security patches are to stop spare phishing attacks against an individual. The days of connecting to the Internet on an unpatched machine and getting hacked are long long gone.
2. Over time, if a machine isn't updated, websites will stop working. They will stop working because either the rendering won't correctly happen because new standards are always being introduced, or security protocols will change (breaking banking and financial websites).
3. Eventually new wifi standards will be implemented, preventing the machine from being able to connected to wifi networks. Try getting a Powerbook 1400c connected to wifi these days.
Once a machine is no longer being patched and updated, EXPECT to get another 2 years of updates from the main web browsers (i.e. Firefox and Chrome), and probably another 5 years of updates after that for long term enterprise support versions of web browsers, and then another 5 years after that for connecting to most wifi networks.
I think if the MacBook Pro Max M1 is taken care of physically, it should continue being able to be used until the late 2030's/ early 2040's.