Yes, you can safely set up a new company file in your QuickBooks Desktop (QBDT) 2019, @bob_nj.

QuickBooks Desktop (QBDT) for Windows 2019 was no longer supported starting last May 31, 2022. This includes QBDT Pro, Premier, and Enterprise Solutions v19 in all versions. Since it is no longer supported, the prompt message for an update is just a reminder and a suggestion in case you want to experience the new features of QBDT. Still, you have the choice not to upgrade.

Although your version is no longer supported, you still can create a new company file. And to confirm, if you wish to upgrade, yes, you no longer have access to your older companies. For the detailed step-by-step process of creating a new file, refer to this article: Create a QuickBooks Desktop company file.

Also, I'd like to mention that the reason why you're being prompted to sign in is to prioritize the security of your account. This is the new security protocol introduced to QBDT software users. 

Additionally, I've included this article in case you'd feel the need to upgrade to a newer version of QuickBooks Desktop: Upgrade QuickBooks Desktop Pro, Premier, or Enterprise.

You can always count on me if you need a hand in managing your QuickBooks Desktop account and company files. Just hit on the Reply button and I'll be right here to assist you.