Is it possible to run a random subset of builds/tests through the pipeline?

I’d like to run a random subset of my pipeline jobs when the pipeline is triggered. Is there a way to do this in my GitLab CI pipeline setup, or is this something that I’ll have to set up backend with my build and test scripts?

Backend for sure in my opinion. You want your CI to be solid and able to count on it performing in a predefined order and flow. So yes, implement in testtooling or backend.