Search Function in finder does not work on my external drive unless the file has been previously opened.(which means it doesn't work)

Good afternoon NalaNosnevel,

Welcome to the Apple Support Communities!

I understand you are trying to search for files on an external drive using the Finder app in macOS Catalina. How is the external drive formatted? Have you ever successfully performed a search on this drive? I've highlighted some key information here for you. Click the link for complete details.

If searching your Mac returns unexpected results - macOS User Guide - macOS Catalina 10.15

"If you began your search in a Finder window, the search results include only files and folders on the internal disk."

How to rebuild the Spotlight index on your Mac

If searching your Mac doesn’t return expected results, rebuilding the Spotlight index might help.

1. Choose Apple menu  > System Preferences, then click Spotlight.
2. Click the Privacy tab.
3. Drag the folder or disk that you want to index again to the list of locations that Spotlight is prevented from searching. Or click the add button (+) and select the folder or disk to add.
4. You can add an item to the Privacy tab only if you have ownership permissions for that item. To learn about permissions, choose Help from the Finder menu bar, then search for “permissions.”

Get to know the Finder on your Mac

Use external storage devices with Mac - macOS User Guide - macOS Catalina 10.15

Take care.

Hi NalaNosnevel,

Thanks for letting us know that your issue was resolved.

Have a great day!