Finder won't load.

Make a reliable backup if at all possible, for instance with a Time Machine disk connected it should run automatically, or tell it to run from the Time Machine icon in the menu bar. Or if you have one already that at least has backed up your files, then you are somewhat protected. If you can get Disk utility to open, the Restore button may also allow you to make a backup.

Was your Time Machine drive the one that wasn't ejected properly? If so, your backup might not be reliable.

Is your mouse connected and working properly? If it isn't, it might look like finder isn't responding.

Boot into Safe Mode, holding Shift key, be patient as it can take quite a few minutes, it is checking many things. Can you do things in the Finder in Safe Mode? Then restart normally and test again.

If still no Finder, boot into Recovery and run Disk Utility First Aid to check/repair the disk. Rerun it until it finds nothing to fix. Then reboot normally and retest.

If still no Finder, boot into Recovery and choose the option to reinstall the MAcOS. This is the option that does NOT INCLUDE erasing or formatting the disk, it simply reinstalls the MacOS, it should not modify or touch your user files.

Then boot normally and retest.

If still no Finder, the next step would be to erase/format the disk and install a fresh system but don't proceed with that yet, you need to find a way to reliably back up your files before doing that. If you have been unable to execute a good backup, one option would be to enable Sharing in the System Preferences and to copy your most important files (I would copy everything in your user directory) to another Mac through the network. Another option is to boot into Target mode and connect to another Mac and copy your files that way. Hopefully one of the earlier steps resolved the issue.

KBinUP Said:

"Finder won’t load.: it started up normally and has been fine since apart from sometimes not displaying a folder on an external hard drive. Instead, it shows two folders with the same name and contents. All folders appear normally when the drive is plugged into my old MacBook Pro. Just weird. Thanks for responding!"

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Things aren't showing up as they should. So, it seems like Finder is corrupt in one manor or another. So, reinstall the macOS to fix that.

Reinstalling the macOS:

Sometimes, changes are made to your Mac (i.e. Updates), and then settings (i.e. for ports), become manipulated, technically. So, reinstalling the macOS will place moved items back to where they should be, and will replace damaged system files. There are two steps: backup, then perform the reinstall. In depth:

1. First, Back up your Mac:

Create a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the reinstall.

2. Then, Reinstall the macOS:

Nothing would be deleted. It's just that items that have become corrupted or deleted, would be replaced or reinstalled back to where they should be. Go Here: How to reinstall macOS from macOS Recovery - Apple Support

KBinUP Said:

"Finder won’t load.”

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Try Safe Mode:

In Safe Mode, login items do not run, and corrupt system files(i.e. caches) are intentionally reset as a way to fix issues

1. Boot: in to Safe Mode: [Hold Down: shift key upon boot].
2. Log in: as same user
3. Perform: the update
4. Restart: your Mac
5. Log in: as same user

In terminal type this below

killall Finder

Finder will re-open

if problem still persists, Restart your mac

Hey there! Are you able to select anything else? Or is Finder freezing the whole machine, not allowing you do click on anything?