A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Dear LuAnn Hogberg
Good day! Thank you for posting in Microsoft Community. We are happy to help you.
Based on your description, it seems that you want to create 2 SharePoint top-level sites using 2 domains in one Office 365 tenant and make another top-level site not associated with the default account with URL not associated with default domain.
If my understanding is correct, this is your scenario, we have to tell you that the answer is NO. You can’t use another custom domain as a top-level site in the same tenant. To use another domain as top-level site, we need to sign up a new Office 365 account. Then we will get the site https: domain.sharepoint.com by default.
Given this situation, we kindly suggest you send feedback to SharePoint · Community (microsoft.com) to make our products and services better for you and others. It is the best platform for us to listen to your opinions and make our products better serve you and others. The user voting here can let us better understand what users want, so that we can better improve our products.
If this is not your scenario, please kindly provide more detailed description to us so that we can clear your query and find the best solution for you.
Your understanding and patience will be highly appreciated. I hope that you are keeping safe and well!
Sincerely,
Stacey | Microsoft Community Moderator