Easy way to tag a PR as "dependent" on another PR


I don’t know if this is the right place to post this, but my team and I have been looking for a way to link two PRs to essentially block merging one before the other is merged as well.

Right now we simply include the link to another PR in the description/comments and setting a “dont merge” label. This is especially useful since we work with multiple repositories that interact with each other, meaning that one feature merge can affect another repository.

Is there a (fast) way to automatically detect if a PR has been merged and as a result update the dependent PR, either with a webhook enabling the merge action, or by setting/removing a label automatically?