I was pretty shocked that most of the ddcutil & other similar programs on Linux weren't working for two of my monitors. The utils couldn't even detect the DDC display. But I told it what i2c bus to send to & what commands to issue, and it turns out my monitors had a pretty wide range of commands.

Reminds me of an i2c motor controller I bought years ago, based off some avr microcontroller. I spent an afternoon trying to understand how I'd hooked things up wrong, trying to understand why I couldn't read the control values. Turns the soft i2c interface just didn't implement reading values off the controller at all, but served ok if I treated it as a write-only device. Frustrating tricky devices. Sometimes they lie.

But yeah, also a >15% chance your monitor doesn't support switching inputs via DDC/CI. Would be so nice if review sites would cover this sort of thing. As it is, it's just a tech-secret, something invisible to the market, no push to include it, no points deducted for getting it wrong/bad. It leaves a lot of room for the situation to sit & not improve. Better reviewing would help move things along.