I recently acquired a refurbished PC with Win 11 Pro installed. Apart from letting it update to the latest version - which was 23H2 (i.e. 2nd half of 2023) I've not used it. Photos behaves as Nigel described.

But there is a version 24H1 and also, I think, a 24H2. I guess the change Joe experiences was in 24H1. I suppose that what version you have and what it updates to depends on your PC - when and where it came from. And 'AI capable' machines get extra AI features.

You can also voluntarily install 'Previews' of the next update - another 23H2 in my case. I don't do that.

My version says (in Settings, System, About):
Experience: Windows Feature Experience Pack
which seems to mean that it bombards me with popups encouraging me to subscribe to Microsoft services. Opening Photos gave me half a dozen.

(Irfanview is not Open Source, btw, but it is free for individuals.)