Transferring the installation of a game from one PC to another using an external HDD is generally not supported for games downloaded through PC Game Pass. Game installations typically require verification and licensing checks with the Microsoft Store and Xbox services, which means simply copying files may not work as expected.
However, you can install the game on the second PC using your same account. This way, you can download the game directly from the Game Pass library on the second PC, which may be more efficient than transferring files manually, especially if your internet connection is slow.
If you have limited internet access, consider downloading the game during off-peak hours or using a wired connection if possible to improve download speeds.
For more information on game sharing and installation policies, you might want to refer to the relevant Microsoft documentation.