mp2884
We've checked this and it looks like you've run setup.exe by using PowerShell without using the full path or ".\" (as we've described it here in step 3: https://docs.microsoft.com/en-us/exchange/plan-and-deploy/deploy-new-installations/unattended-installs?view=exchserver-2019#use-setupexe-to-install-exchange-in-unattended-mode).
When calling the setup.exe in PowerShell without executing using the full path or ".\" under its current directory, Exchange setup process seems to treat the Setup.exe based on environment variable, and the local Exchange installation path will be set as the "sourcedir" and you end up in the described behavior.
Please make sure to run setup.exe using the full path or ".\" to avoid this scenario.