What are your settings like under sampling opt. Adv. Timing if you go into 320x240LB?
My Samsung C24FG73 picks it up as 1080p and works but this particular monitor isn’t great for it as I have to manually set the refresh rate manually and it causes frameskip.
Try raising V. Backporch slightly and see will the image appear. If not then just make sure the settings are the default ones you’re using.
Edit: If anyone knows a way to get 50Hz to work on 3x let me know. I’ve tried the suggestion in the first post of 720p50 settings but it still won’t show on the TV. I guess 3x only works in 60 as 1366×768 is a PC resolution. The TV seems to just use 1080p or 4k for everything else I throw at it on the PC but it always displays them, it just wont accept the inputs fron the OSSC. I was expecting 5x to work since it’s a 4K TV but 3x honestly looks great on it. I just wonder now is there a tweak for 50Hz otherwise I have to play those ones at 2x stretched to 16:9. At least they work I guess but if the TV didn’t stupidly force you to use 16:9 50Hz would be fine at 2x especially with the higher resolution of 288p vs 240p.