Do you mean link multiple PRs across multiple repos? You can already merge multiple commits together in the same PR, in a single repo, of course. via branches.
If so, this can't be done within git, since the overall container is a single repo.[1] There is no atomicity or even coordination between repos. You can get loose coordination though via integration with an issue tracker like jira. The tracker links multiple PRs across multiple repos into a single meta-merge. But you aren't going to get "simultaneous merge" in the sense of a single atomic cross-PR and cross-repo commit.
[1] One of the things that is awful with github [not git itself], is that all your controls such as commit rules, privileges, visibility, have the granularity of the entire repo. Even though awful, this is the right approach considering that many git restrictions are per-repo, eg branches. vs perforce, eg
Yes, I'm talking about coordinating PRs against multiple repos. Obviously, this isn't a git feature, this is something that Github would need to do, just like issues/webhooks/comments are not git features.
This is one of the reasons cited for monorepos, you can make a single atomic commit/PR that changes some API, and the consumers of that API.
As it is now, you end up writing a warning comment to merge some other PR at the same time and hoping your reviewers read it.
If so, this can't be done within git, since the overall container is a single repo.[1] There is no atomicity or even coordination between repos. You can get loose coordination though via integration with an issue tracker like jira. The tracker links multiple PRs across multiple repos into a single meta-merge. But you aren't going to get "simultaneous merge" in the sense of a single atomic cross-PR and cross-repo commit.
[1] One of the things that is awful with github [not git itself], is that all your controls such as commit rules, privileges, visibility, have the granularity of the entire repo. Even though awful, this is the right approach considering that many git restrictions are per-repo, eg branches. vs perforce, eg