Technically UTC isn’t a timezone it’s a reference time that everything else is measured against. GMT is UTC+0.
It would make no sense internally to use anything else if they want to communicate with other countries without issues… the humans yes they’ll use timezones, but the computers don’t care whether it’s dark at 9am so just use the same time worldwide.
(It gets more complex when you’re coding, because APIs seem to randomly talk about GMT and UTC because GMT was the standard when the earliest stuff was designed… as a programmer I just mentally translate them to the same without thinkin but I’ve had people get really upset that I would do that and insist they’re completely different…).
A side effect of this is lots of systems when setup to tick to the next day at 12am either do it at 12am or 1am depending on the time of year… 99% of the time nobody notices this…
Another one that (probably, although I haven’t tried on 11) still works. On Windows create a file, change your date to summer/winter depending on when you did the first file. The timestamp on the file will have shifted one hour (timestamps are stored as UTC but the display functions are stupid and apply the current DST offset not the one valid when the file was created).