Since updating to Monterey can not move files on external disk.

Welcome to the Apple Support Communities.

What error do you see when you attempt to move files?

Have you run First Aid on your external drive yet (Repair a storage device in Disk Utility on Mac - Apple Support), tried in Safe Mode (How to use safe mode on your Mac - Apple Support), or read Connect and use other storage devices with Mac - Apple Support?

Jack

dscruggs Said:

"Since updating to Monterey can not move files on external disk.: How do I clear external disk so I can move files in Monterey?"

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Mount the Hard Drive in Disk Utility:

While booted into Recovery Mode (Intel or Silicon) go to Disk Utility> tap the Hard Drive, then tap the Mount button. See if you can then install it. If it is already mounted, then unmount it and then remount it. See where you can go from there.