Final Cut Pro Missing files, file doesn't appear for relinking

Select Eye of the Tiger in the browser. What does the Inspector say about it? Select the 'i' at the top for Info and set the metadata view popup at the bottom to Extended. Post screenshots.

Open Eye of the Tiger in QuickTime Player and press Command-I to show the Info window. Twirl open all the details and post a screenshot.

Have you tried deleting Render files? Select the library in the browser, choose File->Delete Generated Library Files... Choose All Render files. Manage render files in Final Cut Pro for Mac - Apple Support 

Have you tried resetting FCP Settings? Hold option and command while launching FCP and choose Delete Settings. FCP will open the default Untitled library. Set your preferences back to the way you like (disable background rendering, etc.). Open the library you were working on and see if the problem has been resolved.

How did you import it? From where? Where is the file supposed to be? Inside the library bundle? Were you copying to library on import or leaving it in place? Where is the file? Do a Finder search.

Copy the file to another folder, Desktop, Downloads, somewhere else and try to relink from there. If FCP doesn’t find it, point it to where it should look.

Eye of the Tiger shows the missing indicator. Where is this track stored? Is it from Apple Music? You can’t use that.

Did you copy the file to another location? Does that file play in the QuickTime Player? Can you post a screenshot with just the problem file selected?

In the screenshot, we are looking for "movie folder". Please specify the correct location where the media is stored.

What do you mean by "In the screenshot, we are looking for movie folder. "?

You have specified the "Movies" folder.