Hello, Miles Musicki here from Michigan, US.I think I found a bug in PG 13.4, or at least I can't find a reason why it would behave this way.
My question, as well as explanation what I did to avoid the behavior, is displayed here.
https://stackoverflow.com/questions/70614464/postgresql-insert-into-on-conflict-column-name-is-ambiguous
It has to do with INSERT INTO statement when using ON CONFLICT.
All the best.
Milos Musicki
mmusicki(at)yahoo(dot)com