Oh wow, this actually helped me fix it. I had to downgrade to 1Password4 for Windows (no mention my license only works with that version), and after that I was able to enter my old license key.
By hidden I meant the downloads page is only linked in the footer. All of the main 'Get Started' and 'Try Free for 30 Days' links funnel you into their subscription process. I thought signing into my account might help, but then realized I'm not able to do so in a 'legacy' account because I don't have a secret key.
What a confusing and hostile user experience to 'legacy' license purchasers. It's like they are trying to forget that we ever existed.
https://1password.com/downloads/mac/
https://1password.com/downloads/windows/
I still use 1Password 6 with Dropbox to sync. Works great. If you have a license, you may have the wrong (new) version, or just need to activate it.