No more endearing would normally mean there was a sentence before this, and this sentence is a continuation. First you say something you don’t like about someone. Then you say “no more endearing is ___________ . Meaning I don’t like the first thing, and I don’t like the second thing any better. (It is no more endearing.) To be endearing means something is nice or charming, so it makes the thing or person “dear” to you. If something is dear to you you like or love it. So: you use “no more endearing” in a list of at least two things you don’t like. I don’t know what came before this, but let’s pretend.... “I dislike the way he orders the junior employees around. No more endearing is his patronizing jocularity.” So the writer doesn’t like how the subject treats the young employees at the office. He also doesn’t like his condescending jokes. It does not mean that the writer found the jokes interesting in the past. It’s a pretty negative thing to say, and it would imply that the writer never liked anything this person said or did. This is very much a written language sentence - nobody would speak this way. And “patronizing jocularity” is a complicated way of saying what the writer means, so I would guess this text is from a novel of some sort.

No time for jokes. Come on let’s practice more together