The problem with manually having to close the tab is not the effort required to close it but then mental hiccup it causes when my brain opens my browser and now has to figure out which tab I was trying to go back to

I agree.

My issue with browser extensions is, even if the author and code are trustworthy now, what's to stop the extension from being sold to unscrupulous folks years in the future?

That's fair, but the actual extension <https://github.com/kskashyap94/zoom-auto-close> is like ten lines of code. If you don't trust it not to change into something malicious, create a local copy.

It's just closing tabs after a bit of time, and scoping that code to Zoom URLs...

Agreed, userscripts are the better approach. There's at least three on here for closing the tab, I haven't tested them:

https://greasyfork.org/en/scripts/by-site/zoom.us