It’s possible for a pull request not to match a workflow. This all depends on what your last workflow’s conditions are – if you leave them empty, then any pull requests that don’t match the preceeding workflows will match the last workflow. But if you specify conditions on the last workflow, then any PRs without a workflow will use the “unmatched status” to report back to GitHub.
You can configure the unmatched status in your organization settings. By default it will be “(None)” which means no PullApprove status will appear on GitHub if the PR doesn’t match a workflow. You can configured this to be pending/error/failure if you want to enforce that all PRs must match a workflow, or “success” if PullApprove is a required status check and you want unmatched PRs to be able to merge.