How is the president able to appoint a new VP when there is no vacancy?
"to appoint, with the advice and consent of the Senate, the vice president in the event of a vacancy in that office; (Amended February 2019)"
I suppose the "vacancy" is assumed when Ses announced his intent to resign. Perhaps some more specific clarity could benefit, but there's no short supply of confusing or grammatically incorrect aspects to the constitution, from what I've been able to determine. It doesn't help that the wiki seems really outdated.
When I first ran for office one of the first things I noticed was an affect vs. effect inconguency, though I assumed it wasn't worth pursuing as a full amendment.