ddcvcp VS twinkle-tray

I wouldn't do it that way; opening and soldering in the monitor. I'd go with using DDC and VCP, just hook i2c and GND to the unused VGA port and then use something like this to send a custom VCP command (I think it's 60 to switch).

Yes, in my experience, most monitors do accept DDC commands even if the video signal comes from another input as long as the other input keeps the line busy.

For example, on the Pi this was not possible in past, we had to wait for the vc4-kms-v3d GPU driver to get this functionality. Thankfully it’s beta version coincided with the M1 release :)

There’s no DDC dial available, but it’s something I tried doing in the past using an ESP32 that gets Power-over-HDMI [1] and sends DDC through the I2C wires of the HDMI cable [2]

Unfortunately I had to put that on hold as I started a Mac app studio [3] which took most of my time away. (and I also realized I don’t have the means to sell and distribute a hardware project)

[1] https://www.hdmi.org/spec21sub/cablepower

[2] https://github.com/tttttx2/ddcvcp

[3] https://lowtechguys.com/

Monitorian requires a subscription for hotkeys and CLI, unfortunately.

Twinkle Tray is an alternative: https://github.com/xanderfrangos/twinkle-tray

For example with Twinkle-tray

I found https://github.com/emoacht/Monitorian https://github.com/xanderfrangos/twinkle-tray, but they can't change other settings (color in this case) like gddccontrol in Xubuntu.

Also use brightness adjustment like twinkle.

I achieved this with SWICD and Twinkle Tray.

Easy way to hot-key brightness levels to a keypress, download TWINKLETRAY https://github.com/xanderfrangos/twinkle-tray You can then map brightness up/down using SWICD or JoyXOff to a button press/combination and set % step (i.e. 1%, 5%, 10% etc.)