Please see here for information about the Google Photorealistic 3D Tiles crash and how to upgrade Cesium for Unity to fix it:
@Boris, welcome to the community! Upgrading Cesium for Unity should be a relatively straightforward process within the Unity Package Manager. The link above has a little more detail, and the link to the Quickstart which has a lot more detail. Let us know if you’re still having trouble. Reinterop errors are usually the result of trying to using the GitHub repo directly as a Unity package (this won’t work), or perhaps indicate you just need to restart the Unity editor.