It's been at least 5 months now since the last time I got that annoying popup. Am hoping it's gone for good.

The problem, in my case, turned out to be that I am a former, but not current, user of Quickbooks Payroll Service. Even though I had stopped using that service a few years ago, QB still had me flagged as "Full Payroll", under Preferences, Payroll & Employees, Company Preferences, Quickbooks Desktop Payroll Features.

I tried in vain to click the "No Payroll" box, instead of "Full Payroll", but it wasn't allowed. I contacted QB Support in a chat session and described what change I wanted to make. After giving me some warnings that this step would make it very difficult for me to use their Payroll service again, they gave me a special, temporary code to enter which gave me some elevated privileges to check "No Payroll". And the problem was solved.

So it appears that on startup, QB had been seeing this phantom setting for Payroll in my company, and that was triggering the demand that I log in to their servers. Might apply to other addins as well. If you are actively using QB Payroll then this would not be an option.

Am using QB Desktop Pro 2019.