I noticed this the other day when I installed VSCodium on my new Windows box. I had a functional setup for
one day, then the next day I couldn't install a language extension I direly needed.
It's left a very sour taste in my mouth. I've used Emacs for ages and despite being a much more niche editor, it's never been so hard-dependent on centralized repositories, and the centralized repositories it does have (ELPA/MELPA) are apparently a lot more reliable than OpenVSX. Installing Emacs packages manually from source is a breeze, doing so with VSC is masochistic.
VSC is not really "open source" in any meaningful sense. It is just plainly unusable if you don't do things the way Microsoft wants you to. I do respect the VSCodium devs for trying to make VSC more properly open, but it does feel like a futile effort.