What has worked for me...
On the regular Annual Pass page, there is a link for “Florida Residents and
DVC members”. Click it, and you will have to put in your password.
Then you will see additional options. If I recall correctly, there were tabs. You click on one tab to see the FL stuff and a different tab to see the DVC options. If that doesn’t work, ping back, and I’ll track through it and be more specific.
As BillPA says, you will need the Blue Card to buy the DVC AP. Even if you are able to purchase one online, you have to activate it in person, and they will check eligibility.