How can I actually hide some vaults?

Hello dserodio! 👋

Thanks for reaching out. If you create a collection and then switch to using that collection in the 1Password app, then you shouldn't see vaults that you've excluded from that collection in the sidebar:

• Use collections to create custom groups of vaults

If I select an item in the Autofill popup and choose Open in 1Password, the app opens with "All Vaults."

There shouldn't be an "All Vaults" option in the 1Password 8 desktop app, do you mean that you see "All Accounts"? If you see "All Vaults" then it is possible that you're viewing items in the browser extension or in the 1Password.com web app, both of which don't support collections? Are you able to provide a screenshot as long as it doesn't contain any sensitive information?

I look forward to hearing from you.

-Dave