Same here, also with a 4000 line Swift file. Now I need to redesign my application code around Xcode's problems.

I just got this working. Thank you! Besides waitUntilCompleted as you recommended, I also switched from MTKView to a lower level technique using CAMetalLayer (following an Apple sample project named "CustomMetalView"). That may not be necessary but in my situation it helped. Now when I'm in LLDB and I step across a change in the data model, I can call a certain Swift function (p debugRender()) and I see the change on my device screen. Sweet!

You didn't get the 3 bar icons on the right side, after tapping "Edit". That's odd. I see it on my device. You drag that to move them. As for the circles, I left that to you. Now it just turns the text green, but you can conditionally draw a colored circle using SwiftUI shapes, like Circle.