Activity Monitor and System Profiler won't report 32 bit apps
Support for 32-bit apps was already removed in 10.15 Catalina.
It would make sense that Activity Monitor would no longer have that column since no such apps can run. It looks like that column was also removed from System Report.
So the good news is you probably don't have anything that broke, or at-least you haven't missed them if they did.
If you still want to check for any lingering 32-bit apps, you can probably still do so using mdfind in Terminal.