Hi there, @mac2it.
Let's check why your QuickBooks Desktop (QBDT) for Mac crashes constantly.
Last May 31, 2019, the access to the add-on services was discontinued for QBDT 2016. However, if you don't use any of the add-on services, your product will continue to work for you. If you've experienced issues while working with your QuickBooks 2016, you may need to update QuickBooks occasionally.
For further details, you can check this article: Update QuickBooks Mac Desktop.
If the issue persists, you may have to run the built-in diagnostics and repair tools called rebuild and verify data utilities. These tools comb through, repair, and notify you of data damage within the file.
If it finds an issue with your data, you will be prompted to Rebuild Now or View Errors. Choose Close, then perform the steps below:
If the problem continues, you may need to follow the next steps provided in this article: Troubleshoot Crash Catcher.
That should help fix the issue you're getting. Let me know if you have any other questions, I'm just here to help. Wishing you continued success!