how to set an azure pipeline to run ONLY 1 build at a time

For the life of MS, I couldn't find a way to allow a pipeline to run a single run at a time. Regular pipelines not releases or anything crazy.

No CI, simply to allow the pipeline to run 1 run concurrently. if another run is started it will wait for the currently running one to finish. Something so simple. a simple queue of 1 parallel runs.

Exclusive locks aren't an option since they are at the stage level, so if my pipeline has many stages then each stage waits and they dont run together, i want the queue of runs to be at the pipeline level.

Changing to using a new Scale set of agents with just 1 agent isnt an option. Using demands also too complex. I just want a setting to set a pipeline max parrallel runs to 1, too simple, new runs will queue up and run in sequence.

any ideas?