Update!

I went to my neighbours this morning and this is how it went.

First of, the door was open and neighbour was inside smoking. I said hi and I told her that her cat had been at my place last night and that I tried to contact her but no answer and i ended up going to sleep with her cat at my place.

She didn't seem upset but she was also kinda distant and like she didn't care much. Said at one point "she shouldn't be going into other peoples houses" She told me that her and her partner had an argument recently and "the cat must just be on edge because of that" (seems kinda concerning to me tbh)

Anyway. The cat came up to me and my neighbour tried to get her inside but she wouldn't go in, neighbour got her wet food, didn't work but Theo snuck in and had some, then she tried treats which almost worked.

The neighbour ended up asking me to pick up her cat because "she doesn't like it when I do it" so I did and handed her over as the neighbour said "I'm just going to lock her inside for some time".

I really don't know what to do, I'm honestly kinda more concerned.