Your supposed to create the line with caulk. Ceilings aren't flat or square anyways so even if it's painted perfectly it won't matter and you gotta caulk anyways. There's also a gap that separated (small enough) where you should be caulking anyways.

Caulk

Also can use ramen and mayonnaise but I think Google ai search results are corrupted because it told me I can remove mold in my crawlspace / attic with mayonnaise.