Adding Cesium for Unity via UPM is pretty simple. Check the first step of our Unity Quickstart guide: Cesium for Unity Quickstart – Cesium
If you’d like to build Cesium for Unity via CI instead, you might want to take a look at this comment I left on a similar question: CI/CD Fails After Adding Cesium for Unity – Partial Method and Reinterop Errors - #2 by azrogers