I think it is Not a Problem specific to my profile, as you will find this error screen once you click on the Signin > GitHub button in Glitch.com/signin page.
Thanks for checking in! We have asked our team to look into this. I have added your screenshot to the bug report.
If you want to work on your projects in the meantime, you can:
Create a new account using a different sign-in option (email/facebook/gmail)
Then going to your original account’s projects page and remixing a copies of your existing projects.
Once we fix your original account, I will let you know!