iCloud Photos sets Library to Referenced?
In this thread,
https://discussions.apple.com/thread/255316495
It turned out that the OP's library was set to referenced.
When you turn on iCloud Photos does it automagically set the library to referenced? After all, that is what the iCloud Photos basically does, right? Puts the originals on the cloud and simply references them.
Personally, I don't use iCloud Photos and have no desire too, so this is simply to give advice to other posters.
MacBook Air 13″, macOS 11.6