The Anilist mods aren't absolutely positively sure that the TV series isn't going to be just the movies cut up into 24 minute episodes.
CR being weird about not announcing things the usual way is throwing them off.
https://anilist.co/forum/thread/74026
MAL is saying that the TV is going to be the movies with additional scenes.
https://myanimelist.net/news/71095177
With 2 movies at say 2 hours each, that's about 4 hours, or 240 minutes of footage.
To make 18 episodes of 24 minutes that's a total of 432 minutes.
They save 3 minutes per episode with the OP and ED, so for 18 episodes that's 54 minutes.
So 432 - 240 - 54 = 138 minutes of actual new footage, not including cleaning up, different transitions, editing, etc.
That's an average of 7m40s of new footage per episode
That's quite a lot of new footage.
The closest comparison that I can remember is Demon Slayer Mugen Train, that first came out as a movie, then was split into 7 TV episodes.
The Mugen Train movie was 116 minutes, and 7 episodes x 24 minutes would be 168 minutes
168 - 116 = 52, subtract an additional 21 minutes for OP and ED, and there should have been about 32 minutes of additional footage
That was about 4m34s of new footage per episode.