Dynamo2.3 (Revit 2020.2) Does Not Start

I am unable to launch Dynamo from Revit2020, a blank window opens when I try, Dynamo player works well. I read about the add-ins conflict on earlier topics, and have copied Revit add-ins to a separate folder to disable all of them temporarily, as well as removed all external Dynamo packages for now, but no go!
Have also made sure I have the hotfix for the Revit 2020 version.
Very confusing since the error has come out of the blue. Dynamo is working well on Revit 2019, but Revit 2021 has the same issue.
Any help will be appreciated!