The new submission system went into effect a couple of days ago (July 29, 2019).
You can submit your final project directly on github. You are only required to submit a README.md file describing your project, so the easiest is to do that directly on github.com
First, go to http://cs50.me/cs50x and make sure you are set up for the CS50x course in the new system. (You'll see a Join button if you aren't, so choose that if needed.) This will give github access to your submissions.
Then, go to github.com/me50/USERNAME (where USERNAME is your github username). Create a branch called
cs50/problems/2019/x/project and upload your README.md file to that branch and then Commit. (You can certainly upload your other project files if you'd like, but not required).
Within a few minutes, you should see the grade on cs50.me/cs50x
Be sure to also fill out the form per the spec.