We're utilizing Okta as our autentication source (identity management) and would like to remove the step of entering your e-mail in the Microsoft Login Page. All this page does is redirect to Okta.
We were able to accomplish this in SharePoint: https://support.office.com/en-us/article/Enable-or-disable-auto-acceleration-for-your-SharePoint-Onl...
ADFS should be not supported in PowerApps, there is an idea submittted on this already.
Currently it is only available for PowerApps to authenticate through AAD, which means the Email Account is required.
You may consider submit this as an idea under PowerApps idea forum:
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