Hi Jeff, I've been playing around here, and it seems the Calendar works quite different than a regular entity list.
The main problem I guess is not that it's not filtering by the query string, the problem is that it doesn't even have any metadata filter option for calendar view. I was playing around with Liquid, but unfortunately it also doesn't work with Liquid entitylist object, only legacy rewrite Page Templates, quite annoying.
I found this article from Colin Vermander that has a custom implementation rendering a Calendar view: Dynamics 365 portals: Implement FullCalendar with Liquid – Colin Vermander (wordpress.com)
This might help, but it would be a lot of work
You can also apply JS and remove elements that are not from that GUID from the query string, also might be a bit of work, but doable