Fonts problem

This simply doesn't make sense. The System and root Library Fonts folders are fine, or you'd see the same problem in a different account. The Fonts folder in your user account is empty, so that can't be the issue.

This is just a stab in the dark, but it can't hurt anything to try. Close Font Book. Open your user account Library folder again, and then the Preferences folder. Put the following two files in the trash and restart the Mac:

com.apple.FontBook.plist

com.apple.FontRegistry.user.plist

The main cause is usually one of two reasons, though it could be both.

1. A poorly built font is conflicting with other fonts.
2. The font cache data is corrupt.

To fix the second, do the following:

Close all running applications. From an administrator account, open the Terminal app and enter the following command. You can also copy/paste it from here into the Terminal window:

sudo atsutil databases -remove

This removes all font cache files. Both for the system and the current logged in user. After running the command, close Terminal and immediately restart your Mac.

The moment you choose to restart, hold down the Shift key. Keep holding the key until the Mac asks you to login to your account. Once at the Safe Mode desktop, restart again normally.

This resets/removes Font Book's hidden database files and resets its preferences.

Yes, that's the return you should see in Terminal. The command removes font cache files from the system, then returns to the command prompt. You should restart the Mac immediately afterwards.

Logging in to the ghost/guest user account with no issue pretty much proves number 1. You have conflicting fonts in your main account. No amount of cache flushing will fix it.

Open the Fonts folder in your user account. One way to get there is to click anywhere on the desktop, then hold down the Option key and choose Go > Library from the top menu bar.

Once the Library folder is open, go to Library > Fonts. Make a new, empty folder on the desktop. Move all of the fonts in your Fonts folder to the new folder.

Test again to see if the problem has been cleared. If so (and it should be), then at least one of the fonts you moved out is bad.

That there is a Fonts (Removed) folder means you already ran the Restore Standard Fonts command in Font Book, which was going to be my next suggestion.

At this point, it doesn't really make sense why the guest account works, but your main user account doesn't. If you create a new test account, does it work there?

Okay, that means there's no issue with any fonts in the System or root Library folder. About the only other thing it could be is bad collection files.

Close Font Book if it's open, and any other apps. Go to your user account Library folder again. Open the FontCollections folder. Move all collections to an empty folder on the desktop. None of these are important. All of the default collections are nothing more than samples of how to use collections. If you've created any, they may be the problem.

After emptying out any .collection files, restart the Mac and test again.

Thanks for letting me know that last one worked.

I'll have to remember that for future troubleshooting. In the past, restarting into Safe Mode (as you did earlier) normally removes those two files. Apparently, not anymore.