It “works”, but the post editor isn’t usable.
These issues can be reproduced on Meta if you select an RTL locale for your interface language:
Edit: the issue I’m finding with the composer on Meta seems to be related to GitHub - discourse/discourse-full-width-component: Make Discourse occupy the full browser width.
The issue with user cards can be reproduced on either Meta or try.discourse.org in safe mode.
Also, the user-tip modals are incorrectly positioned for RTL locales in safe mode:
