Unfortunately cloud.drone.io has a fixed amount of resources, so if users queue a large amount of pipelines, they will block pipelines for other users.
We are trying to create more content around running your own Drone server and runners, such as Drone CI Quickstart - YouTube and Run your own Drone CI - DEV Community 👩💻👨💻.
Harness CI also offers a free tier that you can check out here.