I don’t think I watch any modern 30-minute sitcoms.
45–60-minutes ones that have on-going plots that span seasons or the whole show, yes, but not, I think, 30-minute ones. I don’t like to pick favorites, but the recent ones that come to mind include:
Crazy Ex-Girlfriend
..
Oh wait! There are some that are about 25–35 minutes per episode:
Barry
Santa Clarita Diet
Not sure if they qualify as sitcoms though since there is a season-wide plot…
In the past, again I don’t like to pick favorites…
The Mary Tyler Moore Show
The Bob Newhart Show
Fawlty Towers