There's 3 different types, the WAY oversized gold text (quest complete etc), text with blue background (retainer sales info etc) and the generic text spam ('you just did a thing'... but with a queued delay meaning it can spam for ages after doing the thing).

Sadly I don't think there's any way to get rid of any of those, which is annoying since it OFTEN gets in the way of what I'm trying to see.

Please SE, give us a way to disable all of it!