Welcome to the forum!

1) I suppose that you do not have the problem with any other documents than Finale documents - right?

In Other Words: Your problem is isolated to only Finale documents - right?

2) If you have backup copies of your Finale documents, try opening a backup copy.

3) The problem could be isolated to the drive where the Finale documents are saved.

You could try copying a Finale document to another storage unit (e. g. a USB drive).

Then, try to open the copy on the USB drive.

What happens if you open Finale first and then open one of your files from there?

Yes, the problem is isolated to just my Finale documents. And I find it strange that on Monday everything was working fine - then all of a sudden, not.

I have not tried putting the files on a usb...not sure how that would help. If there's something wrong with my drive, wouldn't it affect other documents? (But what do I know....)

Yes, I have tried opening documents both by opening the file first and by opening Finale first - neither way works. I just get the little spinning ball (I'm am now so completely annoyed by that colored, spinning ball!)

We need to know more. all of these questions are important.

Are your files on the internal System drive? What version of Finale created them? You upgraded — from what? What is your MacOS? Did you upgrade that recently and, if so, from what?

I don't what the "Internal System drive" is.

I upgraded to Finale in 2018, so I "think" the file I was trying to open was created with Finale 25. But since none of my Finale files are opening, this might be an irrelevant issue.

MacOS is Monterey. Yes I did upgrade at the end of last year. However, as I said, as of Monday this week (and all of January), I was able to open my Finale files just fine. Then since Tuesday, I have not been able to open any files.

I might have missed this, but other than Finale, do other applications (Word, etc) have similar issues on your system? 

I'm assuming "internal system drive" is your MBP's SSD. How old is your MBP (mine is from 2018, has an Intel chip and runs Finale 27 just fine)? Intel or M1/M2 chip in your case?

Not sure if anything changed on your system, but I'm assuming you've restarted the computer and tried to open your Finale files. One thought: what if you created a new User on your system and started up as that user and then try to open your files? 

David she said,

Yes, the problem is isolated to just my Finale documents. And I find it strange that on Monday everything was working fine - then all of a sudden, not.

So apparently it is isolated to Finale.

Have you tried refreshing your preferences?

This causes problems saving a file but perhaps it can cause a problem opening files. Look to see that your Finale/temp folder is a seperate folder. Best to be in a place where the system OS can't touch it. Check to be sure it is even there maybe it got deleted.

I have never ever had to touch or deal with my temp files. In the old days (90's), since CPUs were not what they are now, one could start up Finale and dump the temp files on a RAM disk, which was waayyy fast for that time. But I haven't done that in two decades now.

By default, the temp files are in ~/Library/Caches. One can move them as desired, but there is no clear reason to do so and I suspect no Finale user on the Mac messes with that.

This is in the user's Library. It's accessible to the OS and needs to be. 

Not a matter of luck. The issue, which was fixed in F26, relates to saving files. Not opening them. And the OP is on F27...

Clearly stated, "this causes  problems saving a file but perhaps it can cause a problem opening files."

When something like this happens, the question is always the same: What changed? Something did.

If this happened after the security updates week before last, then reinstall the MacOS by booting into the Repair Partition per Apple's support bulletin.

https://support.apple.com/guide/mac-help/use-macos-recovery-on-an-intel-based-mac-mchl338cf9a8/mac#:~:text=Restart%20your%20Mac.,built%2Din%20macOS%20Recovery%20System. 

If it happened after installing anything else, do a Safe Boot to repair any system paths and reset caches to Default.

https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac#:~:text=Press%20and%20hold%20the%20power,The%20computer%20restarts%20automatically.

If you store files in Dropbox and ran the update that's being pushed slowly to Mac users running Monterey and Ventura, those files are now in the cloud—make them Available Offline and know where that new offline location is.

Another thing to try is to remove Finale completely and reinstall 27. If you've contacted Support, this is one of their standard recommendations. Do save your work files in a desktop folder first.

https://makemusic.zendesk.com/hc/en-us/articles/115003352327-Uninstalling-Finale 

David perhaps you have just been lucky.

There is a whole tech bulletin about this. I don't have a Mac but it seems it can be a problem to Mac uses as well as Windows.

https://makemusic.zendesk.com/hc/en-us/articles/360001298493-Unable-to-save-files-EnigmaTemp-or-Error-2 

Obliviously the OP has a problem that is a Finale problem. As remote as thus may be it is a simple one to check out.