Your external drive or adapter may have compatibility issues with macOS Monterey, rendering it not showing files properly. Here are my suggestions:
- Disconnect the external drive and reconnect with a different USB cable.
- Directly connect to the new Mac or use a different adapter.
- Update the operating system and retry.
- Repair the external drive with Disk Utility First Aid
- Press Command + Shift + period to reveal hidden files.
- Reformat the external drive on Mac and redo all steps.
Those who need to recover data from the drive can use iBoysoft Data Recovery for Mac. It can retrieve inaccessible files from external hard drives, USB flash sticks, SD cards, etc. This software supports Mac OS X El Capitan and later and is compatible with Intel, T2, M1, M2, and M3 Macs. On top of that, it allows you to preview the files for free.