No More Gaps in bathroom

Gents all,
I have removed a bathroom ceiling and replaced it. The bathroom is tiled to the ceiling, more or less. I have changed from 100mm cornices to squareset, and therefore there is a 1-2mm gap between the top of the tiles and the squareset ceiling. So that small gap shd be filled. The question is, in a bathroom can No More Gaps - no doubt mould sensitive - be used under the paint? Or is there a mould resistant paintable gap filler to do this job? For what it is worth, the bathroom is pretty well ventilated, provided 20-something daughters living at home forever choose to open the louvre window somewhat while taking 60 minute showers ..... but I digress. Soooo ....no more gaps as a filler or something funkier? If so, what is it?

1-2mm? Just use a gap filler. You don’t think it’s mould resistant? Cut in some ceiling paint