• How can I get my 5120x1440 monitor working ?
    With macOS 10.15.7, the Intel video driver that Apple provides for any Intel GPU before the 10th generation isn't able to manage any resolution above 4096 on a single video output lane.

    As such, there's no way to make such monitors work on 13" MacBook (Pro or Air) before the 2020 models (using Intel GPU).
    The only Macs supporting this monitor are the Macs using AMD GPUs (MacBook Pro 15", 16") and the 13" MacBook (Pro and Air) beginning with the 2020 Models (but again, only the ones using the latest 10th generation Intel GPU).

    The only way to get this working on any other 13" MacBook (Pro or Air) would eventually to use an external GPU.
    That's a limitation in the video driver provided by Apple, so it's not possible to change this with SwitchResX.


    With macOS 11, the Intel video driver has been updated to allow native support of this resolution on Intel 13" Macs from 2017 or 2018 and newer. Support for other Macs remain unchanged.
    I advise you to read the whole thread on https://discussions.apple.com/thread/8641919 , beginning on pages 35+


    I don't know yet how these monitors work on Apple Silicon Macs.