The Resource you are trying to access is not available error in Server 2016
Below is the error when you trying to open IdpinitiatedSignon page, You will get the error that the Resource you are trying to access is not available.
In Event Viewer,
In Adfs-properties, you can see that EnableIdPInitiatedSignonpage is disabled. Hence that you’re not able to login
To Resolve the issue,
Run the below PowerShell command,
Set-Adfsproperties -enableIdPInitiatedSignonPage $true
Once done, restart the ADFS Service
Now you can see that you’re getting sign in page.