Hi Anthony
The main Temp folder in Windows is in another location . . .
Open File Explorer, then in the address bar paste this and hit Enter:
%temp%
Can you empty the contents of that folder - you may get an error on the last couple of files - that is OK, those are in use
With regards to C:\Windows\Temp that is the legacy temp folder used for older software on your system.
Yes it is safe to delete the files in that folder. That administrator error is very much reported all over Windows 10, it seems Windows cannot decide if we are administrators or not
Try booting into Safe Mode to delete the contents of that folder . . .