I checked, and there were no hidden folders.
I went ahead and moved the data back to its original drive. I no longer get the error I got before, but now it says that it’s in maintenance mode:
Maintenance mode
This NextCloudPi instance is currently in maintenance mode, which may take a while. This page will refresh itself when the instance is available again.
Contact your system administrator if this message persists or appeared unexpectedly.
I searched for instructions, as it has stayed this way for more than 24 hours. I searched and found this guide: How to easily fix “This Nextcloud instance is currently in maintenance mode”
I ran the command, and it seems I now have access again. I need to figure out what I did wrong and how to do this correctly now. Thanks for your help!