Now, with 2022.2, Undo is recorded as a single Undo operation when exiting Prefab Mode. This results in all changes made to the Prefab being reverted if you perform an Undo after leaving Prefab Mode.
Over the course of multiple releases, the error handling and reporting during scene load (and Prefab load in Prefab Mode) has substantially improved, and will now indicate which Prefabs the errors are related to and/or the GUID for missing Prefabs. In fact, the way we handle missing Prefabs’ assets during scene loading is safer and more stable than before.
In an effort to further improve error handling and avoid introducing bad data into your project, we’ve added a Broken Prefab Asset Type, which will be produced by the Prefab Importer when errors that cannot be rectified are encountered.
The most common case is when a Prefab Variant has lost its parent Prefab, perhaps because it was deleted. In this case, we can’t produce a meaningful Prefab Variant, so a Broken Prefab Asset is created instead. This new asset will show information about what is wrong in the Inspector when selected in the Project Browser. If it’s a case of a missing Prefab parent, then the GUID of the missing Prefab is shown. Alternatively, if it’s a chain of Prefab Variants that is broken, you can go up the chain through the Inspector until you find the Variant with the missing parent.
Source: Unity Technologies Blog