前幾天看到 BetterDummy 這個專案，作者在 M1 上面外接 24" 1440p 的螢幕，但沒辦法啟用 HiDPI，於是就寫了一個軟體來解：
M1 macs tend to have issues with custom resolutions. Notoriously they don't allow sub-4K resolution displays to have HiDPI ("Retina") resolutions even though (for example) a 24" QHD 1440p display would greatly benefit from having an 1920x1080 HiDPI "Retina" mode.
在這之前的解法都有些麻煩，一種是買個 dummy dongle 去騙 macOS，另外是用 mirror 的方式使用：
To fix this issue, some resort to buying a 4K HDMI dummy dongle to fool macOS into thinking that a 4K display is connected and then mirror the contents of this dummy display to their actual monitor in order to have HiDPI resolutions available. Others use the built in screens of their MacBooks to mirror to the external display. These approaches have obvious drawbacks and cannot solve all problems.
作者提供的軟體可以先建立 Dummy Monitor，然後再透過 mirror 掛到實際螢幕上：
不確定用起來如何，但如果之後有需要的話好像可以測試看看...