Ad LTE Band 20: Unfortunately NO, still no (working code) access to diagnostic menu to follow this guide -
https://forum.xda-developers.com/t/...bands-and-services-5g-low-band-on-u1.4182293/
Ad significant changes: I guess that's pretty subjective ...many times described A12/UI 4.0 innovations and everyone has to weigh the pros/cons. For me the most important is bult-in "battery care" 85% charging limit (+security update) ... the others are rather design improvements.
P.S. I'm back on the A11 and still pissed @ Samsung, what the hell is the point of limiting LTE bands on a phone that has been a gift to athletes around the world.