The error message "Unity could not find package manager" typically occurs due to one of the following reasons:
Incorrect Unity Version: Some versions of Unity may have inconsistencies or bugs regarding the package manager, which can cause this error.
Corrupted Packages or Cache: If some packages in your project are corrupted or if the cache that stores these packages is corrupted, Unity might fail to locate the package manager.
Network Issues: The Unity Package Manager relies on a stable internet connection to fetch and manage packages. If the network connectivity is unstable or blocked (by firewall or other security measures), Unity might not be able to reach the package manager leading to this error.
System Path Issues: If the system path variable in your operating environment is not set correctly, Unity can have difficulty locating the package manager.
Based on what's causing the error, you can try one or several of the following solutions to resolve the issue:
Update or Reinstall Unity: If the problem is related to the Unity version, then updating Unity to the latest version or reinstalling it should fix the issue.
Clear the Package Cache: Clearing out the package cache can rectify any corruptions within the stored packages. You can do this from the Unity editor by navigating to
Window > Package Manager > Advanced > Clear Cache.
Check Network Connection: Ensure that your internet connection is stable, and that Unity is allowed through your firewall or any other network security system.
Fix System Path: Make sure that the correct paths are set in your system variables. You can check this in the system environment variables section of your operating system. You should see an entry for Unity in the list of system paths.