I am taking the 100 SwiftUI challange but this is a more general question. My question is about modifiers, is there a reference for of all modifiers and what they modify somewhere?

There is not one list because modifiers can be different according to the type of View you want to manipulate.

Start here for the beginning. At the bottom of the page there are more links.

https://developer.apple.com/documentation/swiftui/view-layout

What @Hatsushira says that different modifier apply to different Views

Another way is to Option + click on the View eg Text and you will get a ? and then scroll to bottom and Open in Developer Documentation and then you can see the modifier that can be used on Text view.

Hope that helps

Thanks to all

@roon asks:

is there a reference for of all modifiers and what they modify somewhere?

This sounds like a splendid idea for a starter project.

Jus' sayin'