Originally Posted by
htcrazy I wonder what this is for[.] I mean besides the usual dri[vel] about bug fixes and stability.
The notes for this update only mention security and stability improvements, nothing else. (The notes mention feature enhancements and bug fixes only in a separate section that talks about what firmware updates in general can include, not in the section that says what this particular update includes.)
It's out now for the US unlocked S21 Ultra as well (G998U1UEU5BULH). The bootloader number has incremented from 4 to 5, so it's impossible to revert to any earlier firmware after installing this one.