Why can't I remove app icons from screen on Huawei p10? How to do it?

If you are referring to the "Hide app" function, this is not possible since it has been removed from EMUI 5.x. - it can be enabled using EMUI Tweaker.

If you are referring to the icons from the home screen, if you are in the "Standard" home screen style, you cannot remove icons without uninstalling the application.

If you switch to "Drawer" home screen style, you should be able to remove all icons from the home screen, except the "Apps" icon that opens the drawer.