I "think" it may use a cookie of some kind for logging in offline...I know you need to have at least one successful Online log in with that same computer in order to log in offline....so Im guessing it uses a cookie or some other type of file that stores log in history.

Thanks very much for your reply, Lisa.  I have successfully logged into 2019 while online, a number of times.  I may just need to call technical support, if I can figure out where they've hidden the email or phone number.

https://proconnect.intuit.com/community/help-articles/help/how-to-contact-proseries-for-help/00/4714

No support email address 😞

Have you tried dumping your cookies/temp internet files, etc? It may very well be some temp file thats generated within the program files itself...Ive never really gone digging.

Well, I just logged in offline and went and searched for which PS files are accessed/modified when that happens and it looks like it's the Olac.ini (I think Olac = online access   ini= information) file that holds the info, but I wouldnt advise editing or deleting that file without recommendation from support.