I have a question about the part of Project 3 where you have to change WeSplit so that the total amout is red if the user picks a 0% tip. I couldn't figure out how to call a function on the Picker selection or anywhere else in the body property, I kept getting an error that my function did not conform to the View protocol. I ended up using a computed property to complete the challenge and it worked perfectly, but I'm still wondering is it possible to call a function within a Picker view, and if so how. Thank you.

No you can not call a function within a Picker(selection: label: content:) because the selection require a Binding variable the label require Text() and the content: requires a View of content to display.

Check Apple Document - Picker.

To you try not to include methods/functions inside the body of the View, It a good idea to have the logic somewhere else, so in your case it was the good ways to do it.