The issue here is your disk format. GamePass games don't have to be installed on your C: drive, but they do need the following:
- NTFS formatted partition
- 4096 byte allocation unit size
Both of these requirements stem from the delta-update mechanism GamePass games use. It relies on some low level features of NTFS to efficiently move data around on the drive during game updates. Changing the external disk to be NTFS / 4KB allocation size will allow you to move games there or set that disk as your default installation drive.
something else at play. some games can install. others give ntfs error. some days same game previous ntfs error now installs. not consistent