Trigger CircleCI 2.1 pipeline by both push and pull request
Pipelines cannot be triggered by both push and pull request
CircleCI's pipelines can be triggered by push by default.
There are some cases that push trigger suits, but you might sometimes want to trigger pipelines by creating or updating pull requests.
If you want to trigger pipelines only by pull requests, then you can do it by enabling Only build pull requests
option.
It is notable that with this option, only pull requests to default branch, push to default branch and tags are the targets. It might be insufficient for your workflow.
In this case, you can create pipelines using CircleCI API from GitHub Actions that is triggered by pull requests.