Even 3.12 will be EOL half a year before RHEL 8's.

And "support" doesn't mean you get the same package selection as the original:

  $ yum search 'python3' 2>&1 | grep '^python3-' | wc -l
  1551
  $ yum search 'python3' 2>&1 | egrep '^python3(8|9|\.)' | wc -l
  279