you can enable "force long display" to always open apps in 18:9 screen ratio.
ps: this will disable the app scaling feature as it'll always be 18:9..
there are other usefull stuff too like disabling LDB app which will free up some ram (about 100 mb). and other stuff..
I still don't quite understand the inner workings of how LG makes the app scaling work. If you switched DPI to <500 via adb it basically stops working, BUT so far I've not seen one app with weird graphics, even netflix: all i have to do is press the maximize button a second time when the video is playing full screen and the black bars go away.