Mac iOS 14.1password 7th version
1Password Version: 7Extension Version: Not ProvidedOS Version: iOS 14Sync Type: drop box
Welcome. Do you have a 1Password membership? In your original post you mentioned you're syncing your 1Password data using Dropbox, which might suggest that you do not. Only 1Password membership accounts have Secret Keys. If you are using 1Password without a membership, and are instead syncing with Dropbox, you would not have a Secret Key to find.
If you do have a membership, and have added it to the app, you can find it here:
I hope that helps!