Administrator can not delete some folders and files !

I'm new to Windows 11, so maybe this is a "feature" I don't know about.

First, all PCs I "support", close to a dozen for family and friends, have the Administrator account enabled. I does not get used very often, but I like having it as a kind of backdoor.

From my many years of supporting mini-computers, workstation and servers (all non-Windows, many pre-Microsoft days) I am used to "cleaning up" after applications have been removed. I removed SignalRGB and found a bunch of "leftovers" so I logged into Administrator to delete these folders and files. I found them with File Explorer, Select, Delete key, NOTHING HAPPENS !

Select again, Right Click, Trash can, NOTHING HAPPENS !

Why ?