Same issue here… I recently obtained my Affiliate achievement and trying the Get Started link takes me to complete the Extensions Developer Onboarding (which has been completed and upon checking/validating all 4 steps show complete).
I’ve reached out to support on 10/14 and received a general message and then replied later that night explaining I need further assistance. As of today (10/17) I still haven’t received a new status as to this issue from support.
I’ve found this thread from researching the following pages;