It makes sense it’s a Vim thing since it’s used in kitty config. When I search for marker based folding as someone else said it’s called above, almost everything I get is for Vim. It’s always confused me why gui-based text editors seem to not have a lot of visually-based features like this compared to terminal-based editors. I guess it’s harder to create a system for user customization in a GUI application.

At least Kate has some support. Now that I know what it’s called I will look into what else is available there.