My rule of thumb is: if you need to do PRs in several repositories to do one feature, your projects are either tightly coupled enough that they should be one monolithic piece of software, or your tight coupling is a problem you should work on resolving.

Requiring multiple PRs to multiple repos to roll out one user-facing feature is fine, as long as your independent modules/projects are not actually interdependent (i.e. one of those PRs will not break another independent repo that lacks a corresponding PR).