i have been back and forth to the US and the EU since mid-sept and aside from everything mentioned above, i'd note:
(1) printed documentation is less necessary today v two months ago provided you have submitted docs to verifly. i started out printing everything which was helpful, but the last three weeks, no one has asked for anything other than verifly and/or the BA document upload service--both of which i always did and never had an issue at check in.
(2) on BA and at LHR, be mindful of your mask. i had a mask hawk in F the other week to LAX, but otherwise people are generally courteous and do not take the pi** avoiding masks on board.
(3) vegas will be different re masks bc of course--terrible americans. but if you are just doing a return to LAS, you should hopefully avoid those terrible americans.
(4) it feels close to normal (well, plus masks) and i hope you enjoy!
(5) de-planing by rows is a god send. unknown about boarding because i have had so many go***mn longhaul bus stands from LHR where it is mostly irrelevant.