I heard Moll was a bit standoffish and complained a lot about his role

I'm going to quote TV Tropes (https://tvtropes.org/pmwiki/pmwiki.php/Trivia/NightCourt) to try to help (https://tvtropes.org/pmwiki/pmwiki.php/Main/HostilityOnTheSet) provide an answer:

As the show went along, John Larroquette and Richard Moll (https://www.youtube.com/watch?v=VJlftUNYvRI) grew to despise one another. Moll (https://www.huffpost.com/entry/night-court-reunion-richard-moll_n_2533176) also couldn't get along with Harry Anderson after awhile because Anderson was close with Larroquette. Reasons for the feud tend to boil down to both sides claiming the other was jealous over who was the true "star" of the show (https://forums.mst3k.com/t/so-the-new-night-court/27181/33). It kept Moll from participating in the 30 Rock reunion (Larroquette had a filming commitment with Boston Legal at the time the show was taped).
Also Moll (who was a classically trained (https://www.spoilertv.com/2023/01/night-court-review-well-80s-are-back.html) actor) had very little patience for the relatively inexperienced actor Anderson, and in general grew increasingly fed up with the ad-libs and goofing around by the other actors on set.

Ohhh wow thanks....apparently I heard the cast got into it a lot during the final seasons