Folks, just a quick apology, I was wrong: I just heard that GNOME’s screen recorder is apparently only meant to be used to create low-quality recordings to be added to bug reports.
(Apologies for assuming it was a professional-quality tool. The screenshots it takes don’t look bad so I just went and assumed the screencasts would be usable also. My bad.)
So please don’t use it to create any actual screencasts or anything. (You can use OBS if you need a real screen recording tool.)