Brave (old) is previous version of Brave that based on Chromium and used Muon (electron fork) for the UI. And Brave Browser is the new Brave with new architecture and using Chromium front-end.
This is part of a migration and development plan that announced a months ago. More https://brave.com/development-plans-for-upcoming-release/
This migration is fixed many issues that exist in prev. version. And the old version will no longer receive support, bug fixes, etc.
Brave not yet reintroduce this feature for the new version. As it’s in early development, the team is actively working on it.
The new version just introduced a couple of weeks ago. And Brave just upgraded it’s user to the new version. https://brave.com/brave-upgrades/
The new version is faster and now it’s support most extensions. So if you need 1Password, for now you can install it from Chrome Web Store.
Hope that can make it clear for you.
Let me know if you have another question.