Is there a term for animes (that are like Nichijou, Pop Team Epic) that have several parts in only one episode?
Afaik there is none.
The closest genre that can fit would be Slice of Life but that's a really big genre to something specific you are looking for.
Maybe this list might help.
This is just my opinion, but I feel that when animated, the 4-koma best maps to sitcom. Basicaly, each sketch is a comedic situation. This translates almost exactly to how sitcoms work, by having different (and often disconnected) situations with same characters.