Seems like a smart way of doing it! I’m not sure I can help you with actually getting this to work based on your data structure, but if it’s working now then keep testing edge cases to make sure your solution fits all your needs.
I can however point out a couple of opportunities to fine-tune your template, although it’s pretty minor stuff and you’ve clearly got the hang of it. No invented syntax hahaha! Here’s how I’d write it, which is basically the exact same thing you wrote, but without unnecessarily setting/getting variables. The only difference is that in theory if there are multiple items in the loop that match your logic, doing it this way could display the shortcode as many times as there are items that match. But it sounds like there should probably be only one match based on what you’re describing, so maybe this isn’t an issue in your use case. I’ve also been meaning to flesh out this comment from Eliot into a page in the docs, but you might want to read through it since this would probably be an opportunity to filter your loop with some attributes in your loop tag instead of using conditional logic inside your loop. It might be the same level of performance, but your template would be a little shorter and cleaner. Anyway, here’s an initial pass to remove the unnecessary variables:
<Loop type=course_recap>
<If field=etudiant_suivi includes value="{User id}">
<Shortcode>[stm_zoom_conference post_id="{Field zoom_suivi}" hide_content_before_start=""]</Shortcode>
</If>
</Loop>