You can use Disk Utility to initialize the external USB hard disk to a normal state again.
Step 1: Open the Disk Utility app on your Mac via Spotlight Search.
Step 2: Choose View > Show All Devices.
Step 3: In the sidebar, select the storage device you want to erase, then click the Erase button.
Step 4: Click the Scheme pop-up menu, then choose GUID Partition Map.
Step 5: Click the Format pop-up menu and select APFS for macOS Ventura and macOS Catalina.
Step 6: Enter a name.
Step 7: Click Erase, then click Done.
After these actions, your external USB hard disk is initialized and you can use it for any file storage purpose!