Can no longer duplicate files, am I stupid or what?

The duplicate and export options may be unavailable in some files if the owner has restricted them

That’s just stupid. I started from a shared design file, indeed, but I’ve made already 3 or 4 copies of it, like a copy of a copy of a copy, and modified it - just discovered a trick where I add /duplicate at the end of the file url and it copies it. It’s just that the duplicate option does not exist in the menu, and I lost a few hours twisting my brain around it.