You're running Windows on an iMac?

Does this happen on all Finale files, or just one particular piece?

On windows 10. It happens occasionally. Yesterday it seemed to be replicable, it happened twice, just after opening the program. Today I can add lyrics but the program freezes when closing the program.

Finale runs perfectly well except when adding lyrics? Correct?

On my 'new' computer Finale usually runs very well. On my last Dell computer Finale never had any issues. I say Finale "usually" runs OK on the new Power Spec computer but occasionally lately I am getting the "Finale has encountered and error and will shut down" message. It does and restarts and recovers my file. Why? I don't know. I don't see anything different but there has to be something Finale is expecting and is not seeing. And, that is your issue too.

Do the simple stuff and make sure all your drivers are up to date. Sound, video and printer. You need to do this manually as Windows does not even though it says it does. Go to each ones web site a check yourself. Also make sure your fonts are installed correctly. Try running Finale al by itself. No other programs or apps running and check for any background apps like your virus software which needs to be current, too.

You can try a clean reinstall but Finale must be completely removed form your computer to do that.

windows 10 on Imac,

Oh wait I just saw this. Are you using a Mac? My suggestions are for a PC running Windows. I have no idea how or what could be the issue with Windows on a Mac. Mac's don't even run their own OS very well so I suspect a Windows partition might  present problems too. If you have a Mac get the Finale version for a Mac. You have access to both versions.