Administrator permissions

I am trying to save an edited spreadsheet, but Excel will not let me do this as it has opened the file as Read Only, and it tells me I need administrator permission. I can save the file on the desktop, but not in the folder I want (And if I then copy the file into the correct place it reverts to Read Only). Firstly I did not open the file as Read only. Secondly, when I checked in settings I am described as administrator!

I have just installed Excel on a brand new PC, running Windows 11.