Thank you @mateithemeisle!
I did what you suggested, each of 1) to 5) steps was already right, but deactivating all plugins did make it work again.
In my case, the culprit was GUTENBERG plugin: I had installed it long ago to try and see whether it could replace Elementor… which of course it can’t (and it gets a 2-star rating on WordPress) but that’s not the point anyway.
Thanks again!
