Of course you are quite right to be cautious about any recommended commands and apps that you are not familiar with.
It can be a security risk, or you could make a mistake if/when using advanced commands and tools.
In this case, sfc and dism are standard tools built into Windows for checking the Windows System files.
They are use millions of times every day by computer maintenance/service engineers and advanced users.
In particular sfc is one of the first things that anyone looking to fix a troublsome computer will run.
Here’s the Microsoft article about using them:
(That says to run dism first, but as dism takes time most people run sfc first to see if dism is actually needed).
If you google either one you will get much, much, more about them.
Bu fair enough, if you are not sure about using them yourself then leave them alone.
It’s puzzling how/why CCleaner is still identifying you system as Windows 10, it’s obviously picking that up from somewhere, but the functions like Software Updater are picking up that it’s actually been upgraded to Windows 11.
If you go to Windows Settings>System>About then what does it say there?
I also wonder which Windows version Speccy (also from the CCleaners stable) would identify it as being?
In the end though as you say your CCleaner appears to be recognising that you have Windows 11 and functioning accordingly; it’s just not saying that at the bottom for some odd reason.
Another thought does occur to me here.
Tomorrow is the monthly Windows ‘Patch Tuesday’ and at 18:00 UCT (7-PM British Summer Time) the latest ‘Cumulative Updates’ to Windows 10 and 11 are released.
It will be interesting to see what your CCleaner says at the bottom on Wednesday, following that Windows update.