In previous version of su pro, there is a command when you right click called align view. So if i select a face on a angled plane, then right click, align view, it puts me perp to that face. However, i have noticed in su pro 2021, it never works. I tried my older install of 2019 on my laptop and it worked just fine. so i know something strange is going on.
Align View command does work in SketchUp 2021. Turn on Hidden Geometry so you can select a single face. As it is, you are selecting a bunch of faces with different orientations. There’s no way for SketchUp to determine which face you want to align the camera to.