This really sucks. Totally unnecessary for Google to mess with useful stuff like immersive mode.
Don't know if this will be beneficial for you, but there is a Magisk module + terminal emulator command the fills the entire screen when in landscape. Still can't reliably and fully disable the status bar but it's better than nothing. Even has a Tasker task to make an on/off toggle in the new android power menu.
Not ideal in portrait mode as it messes with the status bar pushing icons even further to the left, but in landscape it's great.