I started getting sure that .world will never update their software and I don’t want to use super outdated software.
I want to move my communities from .world piefed instance to feddit. online, is there is a way to do that without losing subscribers or posts?

The subscribers is the big issue. If we could automatically move over subscribers then maybe PugJesus would still be around.
What happened to pugjesus?
Its pretty much not feasible unless all the devs work together on a compatible method. I looked into it pretty thoroughly with PyLova and while I could get something working PyLova to PyLova it wouldn’t help with anyone subbed from Lemmy or Mbin, etc.
You need to be able to verify the requests from both ends or else you end up with a system where a dodgy instance can just subscribe you to their communities against your will.
Oh, I was just pipe dreaming. Maybe one day, though.