Sorry for the late reply! Yeah, this issue has been going on a while, I believe it was just as present in unity 2020 as it is now in Unity 6. No worries on not testing with other packages lol, totally understand. Not sure if it is the render pass event thing, but that's the only thing I could think of as to why the outline would look normal in editor but different in build. I'm not super knowledgeable on this kind of thing though, so if anyone smarter than me has an idea please do lemme know!
p.s. is there any update on Render graph support? Just upgraded to Unity 6 and had to disable it as instructed.