How do I list the directories/file on my local drive?

OK, I understand now. I can remount the unmounted drives from here:
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I thought once the drive shares are unmounted they are removed from the list at Datacenter > Storage. You are saying they will still be there and only disabled. Got it. Thanks. I will install DerDanilo/proxmox-stuff and try to backup PVE beforehand just in case things go sideways. I'll let you know how it goes.

JUST FOR THE BENEFIT OF ANYONE READING THIS THREAD THIS IS THE PROCEDURE I'M USING:

1. STOP every container and VM individually from its UI desktop using Shutdown > STOP .

2. Unmount drive shares:

unmount /mnt/pve/ISO_Storage
AND
unmount /mnt/pve/Synology

2. Check df- hT to make sure that Synology and ISO_Storage mounts no longer appear.

a. if necessary and if df- hT still shows that Synology is still mounted then unmount the other Synology related shares listed at /mnt/pve/ using:

unmount /mnt/pve/SynologyDS923

unmount /mnt/pve/Movies

then recheck df -hT. Hopefully that takes care of the issue.

3. In the shell use gdu / and navigate to /mnt/pve/ and then to anything that is listed there to see what files exist.

4. Deleting files.

4a. You cannot delete files from within gdu so you need to quit q first and then from the shell navigate to the directories containing the target files and then delete the files.

4b. To delete the file named myfile, type the following:

rm myfile

4c. To delete all the files in the mydir directory, one by one, type the following:

rm -i mydir/*

(Note: After each file name displays, type y and press Enter to delete the file. Or to keep the file, just press Enter.)

4d. Exit the shell.

5. Navigate to Datacenter > Storage and highlight the unmounted share and click Edit.

In the pop up check the Enable box then click OK. Do this for every unmounted drive listed.

5. You’re done!