How to properly sync fork and main repo?

Question

git

There are 2 repositories, one is the main one, the other is its fork.
Both repositories are currently under development, while only their differences are added to the fork, which are not needed in the main repo.
The question is, how easy is it to push commits from the main repo to a fork?
At the moment I’m doing a rebase, but I’m tired of solving a bunch of conflicts periodically and it feels like this is not the right way, and I don’t really want to pick all the commits. you have to look for when they start to differ.