Hello @irsmun,
Thank you for posting here in the Community space. I'm here to share some clarification about QuickBooks Desktop Premier 2019.
You're right. We no longer provide services for our discontinued products like the 2019 version. Also, discontinued versions won't receive the latest security patches and updates.
You can visit some e-commerce stores for users selling older versions. We can't suggest a specific site, but there are suggestions online to give you ideas.
QuickBooks Desktop Premier allows up to 5 users, and Pro allows up to 3 users to work in a company file simultaneously. For more information, check out this link: Add a user license to your QuickBooks software.
Additionally, you can add, edit, and troubleshoot QuickBooks Desktop Pro and Premier User login and restrictions. I've attached an article to learn more about the steps in QuickBooks: QuickBooks Desktop Users and Restrictions.
Let us know if you still have more questions about adding extra users. We'll be around to help out. Take care, and have a great rest of the day.
