I've never seen an IDE "mandated", I've seen officially supported development setups where you're on your own if you do anything different. Is that not the standard?
I've literally never seen this and I've been around for awhile. There's always people with some bespoke vim or emacs setup while everyone else is just using Jetbrains or VSCode or whatever, and nobody cares at all as long as that person is getting their work done.
I'd never have worked at a place that mandated a specific IDE. Luckily it's something I never encountered, if it's ever done this is the first I'm hearing about it.
No, it never occurred to me that anyone would care. I don't think many of my bosses or teammates could have named my choice of IDE/editor even after working with me for a while. I'm sure I mentioned it occasionally but I don't think anyone would care enough to remember.
I was usually most productive with a text editor as opposed to an IDE but I'd sometimes use an IDE as needed or when I wanted to try something new.