The few times when I tried to use a recent version of Photoshop, however, I could not figure out even basic stuff like layer masks,

There are many many more but start with the app having the overbearing assumption that it thinks you want save to its file format rather than make an ad hoc edit.

That's the problem, you have a bias because you've already learned the tribal knowledge. Having to learn it from scratch, GIMP's UI is sorely lacking. While it does have the tools, the organization of them is all over the place.

The big remaining thing I can think of is the "layer boundary" thing, which (it seems to me) is very confusing for new users and inconvenient for all users.

I also have a vibes-based feeling that when I used to use Photoshop twenty-five years ago I was a lot more productive than I'm able to be in GIMP, but I can't be sure if that's just because I used to do more graphic stuff back then and I've never picked it up to the same degree. I find myself having to hunt for things in menus a lot, but that might be a me problem. Photoshop also took a while to get used to.

Edit: I basically agree with the people complaining about Save and Export being unexpectedly separate, although I also think it's not that hard to press Ctrl+E instead of Ctrl+S.

Then one day, they did it. They put the tools on the same window as the image, as Deluxe Paint did in 1985. FINALLY.

... but at the same time, they introduced the absolute bollocks that is "if you hit save we're going to spam you indefinitely into using our format".

In any other tool, if you _open_ a file (e.g. a PNG, JPEG, or in say LibreOffice's case, a CSV or XLSX), and then hit "save", it can nag you once that you're not using the tool's preferred file format, and _may_ be missing some important feature that only its preferred format supports... but you should just be able to click "fuck that, save it as the format I loaded it as" and not hear that again.

Not GIMP. It fucking well refuses to let you save as the format you opened. You have to cancel your "save" of the file you opened, and instead "export" to the file you opened... at which point it warns you you'll overwrite THE FILE YOU WANT TO SAVE. And after you've done that, and try to close the image, it'll warn you you haven't saved THE FUCKING FILE IT JUST FORCED YOU TO USE "EXPORT" TO SAVE because you didn't save it in its preferred format ABSOLUTELY GO FUCK YOURSELF, GIMP, I AM NOT GOING TO SAVE AS XCF A JPEG I AM CROPPING AND WILL NEVER EVER EDIT AGAIN

This is why I completely gave up on GIMP and will never open it again. I would like to line up all the GIMP authors in a row, and run down the line slapping them all in the face with a wet trout.

If anyone from GIMP is listening:

    * User opens a non-native format, e.g. JPEG
    * User hits "Save"
    * Present user with a dialog like so:
        This image may contain content that cannot be saved in the currently selected file format "JPEG"
        Use the default XCF file format to be sure the image is saved correctly
        [x] Ask when not saving in XCF or default format
        [Use JPEG format] [Use XCF format]
    * User can turn off this nag globally by deselecting "Ask when not saving in XCF or default format"
    * If user selects "Use JPEG format", future saves of this file will not nag again