Hi Stevepeters,
I see that you have the Adobe Sign individual account.
The Integration feature is only available with the Enterprise level accounts.
Yes, recently the Adobe Sign interface changed for the individual accounts.
You may refer this help document New Send for Signature experience in Adobe Document Cloud to check what new changes occurred to the interface.
As you have created a new developer account and still not able to create an API key for integration.
You may refer this help document Integration reference guides | Adobe Sign. Check if that helps.
If you still need help, then I would suggest contacting the pre-sales team.
They will check the setting of your account and will be able to provide you with the technical assistance with the developer account.
Please refer to this link Adobe Sign plans for individuals and businesses | Adobe Document Cloud to get in contact with them.
Let us know if you need any help.
Regards,
Meenakshi