Other file managers such as Thunar automatically hides not just dotfiles but also the folder /lost+found when not showing hidden folders. I find this convenient since /lost+found is never really used but is nice to have for security reasons.

How can I hide /lost+found in Dolphin?

EDIT: By hiding, I mean making it invisible in Dolphin, not putting a dot in front of the name. If you don't understand what I mean, try to install Thunar and see what it does in the / folder.

It depends where that folder is located...
generally--because I only find that on my external drives--I change the ownership (from root to my user)
then one can do whatever after that (like hiding it)...