Is the problem document specific - or does it also happen if you create a new document (e. g. a Document Without Libraries) ?

Your suspicion is unfortunately correct. MakeMusic said that older versions of Finale are not compatbile with 10.13. Only Finale 25 and 26 are.

"As of September 25, 2018 we consider Finale version 25 fully compatible and supported on macOS Mojave. All previous versions of notation products prior to this are known to have compatibility issues and we do not expect these to provide good results. These versions are not supported on this macOS.
Finale version 26... will fully support macOS Mojave."

No it isn't document specific and does happen when I create a new document.

And it works at all?

There are a few things to try. The easiest is to change the notation font to another.

Notes appear with stems only but they play back correctly. 

I tried changing the document default font and still there were no beams. 

Appreciate your thoughts and suggestions!

Thanks.

John

It’s still a font issue. Finale used to install in the (users) Library. Now it installs them into the main Library as should all fonts since OS 10.7.

Try this first

https://makemusic.zendesk.com/hc/en-us/articles/217585418-Music-fonts-display-incorrectly

… I tried changing the document default font and still there were no beams… (John Erskine)

… It’s still a font issue… (Mike Halloran)

As Far As I Know, beams are not font characters.

How can the {missing beams problem} be a font issue?

I tried the suggestions in the link from Mike, but they didn't solve the problem. (However I did learn more about how fonts are managed on the MAC.)

Thanks again for your suggestions.