External monitor goes no signal on Fedora 42 when its correct resolution is chosen

ChatGPT is full of nonsense. The point of using an HDMI 2.1 cable, even for an HDMI 2.0 connection or resolution, is that the HDMI 2.1 cable has more bandwidth and much higher spare bandwidth. HDMI can sometimes be a confusing and weird standard; things often make zero sense regarding why something works or not. However, you can’t go wrong with better cables (though there’s no point in spending a fortune on them either).

That being said, I looked up your monitor’s datasheet - https://aoc.com/api/download/20445. According to the HDMI specifications, it can achieve a maximum resolution of 2560x1440 at 144Hz with 8-bit RGB (no 10-bit). So, you may need to ensure that you’re using the correct color space as well.

But probably what best would be to get a USB-C to DisplayPort cable (also known as Thunderbolt, NOT Lightning, to DP); it’s actually inexpensive (around $20).

If a cable has the HDMI logo on it then it will be of sufficent quality.
To get the right to use the logo a company must pass the acceptance tests for the level of HDMI they claim.

hat’s definitely not how it works in practice. Go search any HT forum, and you’ll find many people experiencing compatibility issues with different TVs, monitors, consoles, PCs, AVRs, cables, and more. The HDMI certification process has been called into question many times, and in fact, the common way of referring to cable types (by HDMI version) is banned by the HDMI Licensing Authority; yet it continues to be used by manufacturers. It’s a mess.

If you’re interested, you can read more about it for example here: When HDMI 2.1 Isn't HDMI 2.1 - The Confusing World of the Standard, "Fake HDMI 2.1" and Likely Future Abuse - TFTCentral, but you will find many more articles like this.

The usual recommendation is to stick with higher-quality certified cables for maximum compatibility (that would be a certified Ultra High Speed HDMI cable / 48.0 Gbit/s cable, commonly and incorrectly referred to as an HDMI 2.1 cable).

thanks for the help guys i appreciate it a lot, i will get one better cable tomorrow USB c to DP since anyways it will serve me for higher refresh rate.

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i was confused about this HDMI cable since it came in the pack and worked on windows. Either windows is using some technology like i read (DSC) to compress and make it work or the fedora makes things weird. I still cant figure out if its a good cable hahaha

If it was on the same machine (which actually matters a lot, especially with lower quality cables), it could be anything—DSC, different color space, or bit depth (which changes bandwidth requirements). Who knows? But yeah, I think the USB-C to DP will be best anyway.

edit: Actually, never mind; it can’t be DSC. It is HDMI, which is part of HDMI 2.1+ for higher resolutions.

Thanks for the solution, it wasnt the Fedora which caused the problem. I bought usb c to dp and now achieve the correct resolution and max refresh rate !

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DP is always preferable to HDMI, but it should still work as expected. Could you try again with the kernel 6.15.4 that was pushed to stable today?

i will update now and tell you later. I will check now the available updates in discover

everything works fine on the new kernel

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