The math from general relativity is crystal clear. It’s just difficult to translate into natural language, because it doesn’t match our intuitions, which are primed by local experiences of non-curved space. You have to question your intuitions, and if you’re serious about it, look into the actual math. It all follows from a few basic assumptions, and is consistent with actual observations to an unmatched degree.

To paraphrase Feynman, I can't explain to you how the universe expands in terms that you are familiar with because I don't understand it in terms that you are familiar with.

https://www.youtube.com/watch?v=MO0r930Sn_8

It takes effort to understand those fundamental terms, so if you want to understand this, you'll have to meet people halfway instead of rejecting how somebody is trying to explain something to you.