I don't see why merge conflicts would be a pain specific to monorepos. The merge conflict arises when you and some other person modify the same parts of the same file. No matter the repo size the correct solution here is figuring out the intention of the other person by reading their change or talking to them and deciding how to combine it with your change.

The only reason which may make merge conflicts happen slightly more often in monorepo (vs constellation of small repos) is that not having the repo cloned locally is an obstacle to make the change. So some folks won't bother contributing repo that they'd have to clone first and instead they'd file a bug to the owners.

If you get a merge conflict in a piece of code, you must have touched that code. And if you were capable enough to modify the code to begin with, you should be able to solve a merge conflict around it.