I see this being more useful on mobile platforms but it definitely can be implemented in desktop as well.
There should be an option for secure tabs that can be unlocked with a password/pin/biometrics. This secure tabs area would include both regular tabs, and private tabs. It’s like having a separate brave browser instance running that is password protected. I have a bunch of nieces and nephews that I sometimes let use my phone, and have had a few times where tabs were closed that I needed and I had to go through my history to find it.
It could be like where on certain desktop os’s, you can have “multiple desktops”, but you can password protect them if needed.
There should be an option that you can choose whether or not these sessions can be previewed or not.