FCPX Stuck on loading/validating Library

Where is the media stored, inside the original library on the external or outside?

What OS and FCP versions is this? Has anything changed in the system recently?

Put a backup in the Public folder, create a new admin user, and log into it. Can you open the backup from there.

Please post an EtreCheck report  https://etrecheck.com  giving the application full disk access from  System  Preferences. When it finishes the scan, click Share Report and choose "Copy Report"; then paste in the additional text box in your reply. 

Things I see:

CleanMyMac is installed. This probably means you have to reformat your startup drive and reinstall the OS, then only restore your documents and user items from a backup and reinstall applications by downloading fresh copies from the web. Others will chime in on this.

Chrome and its Keystone daemons have been installed. They can wreak havoc with the ProApps. Completely uninstall the app and the other cruft by following the instructions at https://chromeisbad.com

This drive looks full:

disk4 - WD My Passport 2606 1.00 TB

External USB 5 Gbit/s USB

disk4s1 - EFI (MS-DOS FAT32) [EFI] 210 MB

disk4s2 - W*********l (Journaled HFS+) 999.83 GB (995.16 GB used)

So it sounds like something is corrupt in the library. You could try going into the library package (quit FCP first) and one by one, methodically move each event and the flexolibrary into the trash (do not empty the trash!), then try to open the library. You need to quit FCP before each move, then move the event and flexolibrary, then relaunch FCP to see if you've isolated the corrupt item.

I'd copy that library off to another drive and do the work on the copy just to make sure you don't accidentally delete something.

For the future, I noticed your EtreCheck report says you've got no TimeMachine backups configured. Maybe the drive was disconnected while you're trying to sort this library thing out. But if not, since you've got clients, you really should have a backup mechanism with TimeMachine or CarbonCopyCloner or something like that in case your internal drive takes a vacation. You don't want to lose all your FCP backups.

The drives are badly overextended. The external OS at the point it’s likely to fail.

As Terry said you have problems with CleanMy Mac and Chrome. and likely need to rebuilt the system. Difficult when there’s no backups.

You could try making a copy of the library onto a new drive and seeing if you can rebuilt the library by copying the components into a third library. That’sa real long shot.

The problem may be only showing in one library, but you have systemic issues that likely caused it.

You could try a Project Verify it it reveals any clues.

While holding the Option key select the Clip menu:

Al

Try opening a backup. The library was on the external; was the media stored in the library or outside it?

In addition the system drive is pretty much full, which is always a problem.