First thanks a lot for taking the time to share your results.
You suggest that the problem could be solved by resetting the mac, I have already done that a few months ago with Catalina only for the problem to reappear even after big sur upgrade.
So please, could you try to delete some files locally and inspect if the change in size of the folder is registered and tell us the result ?
That would be very helpful because, resetting my mac a second time would be rather painful and this time I want to be sure it is helpful.
Also, if it ever caught the attention of Microsoft software engineers :
Big Sur does not fix the problem.
I have installed Big Sur, but the problem is still there, see attached image.
As you can see, I have made a local copy of one of my folder which is on the cloud, then I deleted some files locally.
After verification, the files were also deleted in the cloud, and the size of the folder on the cloud diminished, however the size of the folder remained the same locally.
I have waited 20 days, expecting that Mac Os could register the change in size but 20 days later the problem is still on.
