TL;DR

For the impatient (and me):

Set Auto Power Off to 1 Min

Problem: Camera still shuts off in Webcam mode

You're on a Zoom call or whatever using the Canon EOS Webcam Utility, and after about (exactly) 30 minutes your Canon EOS Rebel T5i / T7i / T8i / whatever goes blank for a second (and comes back if you're lucky).

This is because, in video mode, the camera normally turns off after 30 minutes - a silly restriction that's in place to satisfy an ancient European tax classification distinction between video and still cameras.

Solution: Set Auto Power Off to 1 Min

One weird trick...

Intuitively, you'd think you want to set the Auto Power off to 'off' / 'never' / whatever-it-is.

However, counter-intuitively, the solution is to Auto Power off to a low value, such as 1 minute.

I think the way this works is essentially by having the Webcam utility and Auto Power Off fight against each other and constantly reset the 30 counter.

A word of caution: This may be a "bug". Probably best to not update your camera firmware unless there's a really good reason. There have been a few Canon firmware updates that had no useful changes and only "fixed" this sort of thing in the past (re: Magic Lantern).