Prior to 2021 (or is it 2022), the promised support for Samsung phones was 3 major Android (usually one major release per year) releases and one year extended security updates. Since your phone was officially released in August 2020, the promised support period has ended AFAIK.
back panel always heat is normal, because your internal component working properly, not only playing games, a simple scrolling IG can also generate heat from your back panel
i never seen a phone manufacture that has a warranty about their phone never getting heat, so a little heat still acceptable as long as your phone never shut down itself.
Anyway a new update won't reduce your Note20 heat, who knows new update might make it even worse, so be grateful your Note20 still working properly
