@gogetakame said:

Abbott Elementary Season 3 premiered with a two part episode (2 episodes).

This season premiere with a single double-length episode with a composed title. (A 2 part episode is an episode that is broadcasted in 2 separate parts).

IMDb and other places have two distinct entries for this episode as episode 1 and 2, but TMDb has made it just one episode entry. The next episode number is episode 3, which isn't "intuitive".

We follow the listing of the broadcaster.

1. Can we split up this Season 3 2 part Episode into 2 episodes?

No, we can't. It was released as one single episode by the broadcaster.

1. Is there a way to get the exact episode number of the next episode via the Episode API: https://developer.themoviedb.org/reference/tv-episode-details

No.

1. Is there some way to indicate that this episode is a 2 part episode?

This is a double-length episode. So, you can use the episode duration to know that it is longer thah the other ones. But that doesn't give any informations on the number of the next episode. Some series skip number 2 in that case, other don't.

Some way to know that it actually has two episode numbers 1, 2.

There aren't 2 episodes numbered 1 and 2. This is one single double-length episode numbered 1 with a composed title.