Thanks for the Insight,
I already knew about system-tools/I2C from my argon one case. I had tried the Ubuntu package, which didn't work for me (maybe OP there was not using an RPi and thus had access to libX11? It is dynamically linked). My build fails on libjansson, which is not something I will find in LE. Static linking is a good tip, but so far I couldn't make the exe build with static linking. I will ask about that on the ddcutil side.
I also briefly went the 'Fine, I'll do it myself'-route, since there are python-bindings for DDC/CI. The backend seems very doable, but with monitor-selection being a dynamic scan and capabilities being monitor-dependent, I couldn't figure out a good settings-UI fitting Kodis static UI-framework.