The ^[[27;6;63~ looks like xterm's modifyOtherKeys feature, which is not recent.
That's odd, because there was a recent change to vim in this area, but not to xterm. The question mentions this:
VIM - Vi IMproved 8.1 (2018 May 18, compiled Nov 24 2019 15:10:11)
but does not mention the xterm version. The relevant changes in xterm were only for ...