The target principal name is incorrect. Cannot generate SSPI context.

• The SQL Server and instance names are entered correctly
• The specified SQL Server instance is not configured to use dynamic ports
• If a firewall is enabled on the SQL Server, inbound rules exist to allow connections to the correct ports
• The account used to run Setup has permissions to connect to the specified SQL Server instance”

As instructed, I verified all those items without success. My next step was to look at the ConfigMgrSetupWizard.log which was showing this error:

“The target principal name is incorrect.  Cannot generate SSPI context.”

A quick search informed me that this was likely a result of an incorrect or missing Service Principal Name (SPN), which reminded me that just before the SCCM install, the service account for the SQL server had been changed from a local system account to a domain user account.

So, I removed the SQL SPNs from the computer account and added them to the domain user account. See https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-R2-and-2012/cc731241(v=ws.11)?redirectedfrom=MSDN for more information on how to do this.