Thank you for following up on this and I'm glad that you were able to resolve your issue!
Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution in case you'd like to "Accept" the answer.
After following the Single sign-on (SSO) quick start documentation, you ran into the below error message. The issue was that you tried to execute the script
npm run configure-sso and logged in with the demo admin account.
It looks like the application '<<id>>' you are trying to use has been removed or is configured to use an incorrect application identifier.
You resolved this by adding a M365 tenant and logging in with your real account.
Thank you again for your time and patience throughout this issue.
Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.