Minimize button is not active

Yes, the "Minimise" button is grayed out in Full Screen mode, also the menu command and the keyboard shortcut are not active. You can only Quit Photos or exit Full Screen Mode. You have to exit full screen mode to minimise Photos.

You need to move the cursor to the top of the screen so the tool bar will show up:

That's because you're in full screen mode and the only option is to exit it. Minimize is only valid in normal (non-full screen) mode.

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Exactly, OT 😊 - that is what I wanted to confirm. Full screen mode is now limited. Probably because it caused too much trouble, when we could minimise applications directly from Full Screen mode. I never use it anyway. It us bad enough, that many applications open their windows automatically hogging the full screen, instead of remembering the smaller window size I have been using the last time.

I don't use full screen mode either nor minimize. I use hide and have a Keystroke Maestro macro setup so I can hide any app I'm in with an easy key combination.