SSO login for a SaaS application using myapps

Trying to understand the URL specifications or what is happening on a SSO login to Workday and Oracle. On-premise AD is sync'd to Azure AD and IDP for Workday and Oracle.

The default url for access we were using was

https://myapps.microsoft.com/signin/Workday/guid1_removed
https://myapps.microsoft.com/signin/Oracle/guid2_removed

Most users just float in as expected, no username or password prompt. Some users though, are prompted to select a user account from the "known logins" and this is the issue, we are not expecting this.

If we use the following URL then it floats in as expected.

https://myapps.microsoft.com/tenancy.com/signin/Workday/guid1_removed 
https://myapps.microsoft.com/tenancy.com/signin/Oracle/guid2_removed

Wondering why we are being challenged on some clients to select an account?

Is there any documentation on the makeup of the URL for myapps?

Found some on https://docs.microsoft.com/en-us/azure/active-directory/fundamentals/customize-branding allowing for a known landing page with Company Branding where I assume the ?whr= is the Domain Hint as per the Custom Login Page

https://myapps.microsoft.com?whr=MyTenant.com

Where MyTenant is my branded site.