Since Post-processing effects don’t work on LDR mobile target, is there any other way to tint the whole screen?
I have exhausted nearly all possibilities for this issue. Intuitively, with post processing, tinting the screen via a separate pass is the most effective way I can think of to tint your whole screen. However, as you stated, with LDR PP is not supported and therefore this option is not viable. There are other ways through lights and incredibly unintuitive work arounds such as adding a spring arm component to your character and attach a camera to that. From there you could add a cube to follow in front of that camera but behind the player and add an opacity to that.
I would not recommend these work arounds and would say that there is no good way to tint the entire screen without PP effects and HDR for mobile.
What do you think about semi-transparent solid-colour fullscreen UMG widget?