I am quite sure that GitHub uses the same counter for issues, pull requests and discussions.
If I create an issue in a fresh new repository, its number would be #1. Then, if I want to create a pull request, the number assigned to it would be #2. Similarly if I then create a discussion, its number would be #3.
I just wanted to get some sort of confirmation for my guess but couldn't find any in the GitHub docs.
Can someone confirm this?