I cannot deploy the rails project to heroku.

Must see if you're frustrated!How to publish the Rails app on Heroku

I am trying to deploy heroku by referring to the url above.

Now that I put ruby version 2.7 in it,

I can no longer create a blog app to create with scaffold.

Also, due to the difference between ruby and gem versions, deployment is no longer possible.

Which version and what can be rewritten to make deployment possible?