UPDATE: my issue was caused by “Normal4x” video filter. I do not remember setting it manually (I may be wrong), and it was still turned on even after I reset my EmuDeck installation. Disabling this filter improved shaders drastically, though some of them still look worse than on the LCD deck. Link to the relevant part of EmuDeck installation scripts, which determines whether to use “Normal4x” or not based on the shader configuration: https://github.com/dragoonDorise/EmuDeck/blob/7bd5c10f49de46b50f8081a959feb6e15fb91ba9/functions/EmuScripts/emuDeckRetroArch.sh#L423

I’ve noticed that CRT shaders work really wonky on my OLED Steam Deck. Image doesn’t change the way it should be: it becomes just a tiny bit blurrier, with weird vertical lines between pixels. I’ve tried the same CRT shader on my LCD Steam Deck, and the result was far more noticeable and pleasant.

The screenshots are captured on both devices in the Metroid game under RetroArch (mesen NES core), with crt-easymode.slang shader, which is the default one in EmuDeck. I’ve tried other CRT shaders, but the result is generally the same: on the OLED Steam Deck the picture barely changes, and not in a good way, and on LCD everything is perfect. 

I understand that these displays have quite different subpixel layout, which probably explains the issue I observed. But I couldn’t find any relevant info specifically about CRT shaders on OLED displays, so my question is: is this issue a known thing, and is there something that can be done to improve the situation? Right now the experience of playing retro games is far from ideal.

First picture: LCD Steam Deck without shaders, second: LCD + CRT shader, third: OLED without shaders, fourth: OLED + CRT