Idk, with I2C if it’s not something that needs a kernel level driver, there usually isn’t a problem with interacting with it from user space, for example basically all RAM RGB controllers are I2C and OpenRGB has no problem with them. I’m pretty sure I’ve only ever used an I2C device tree overlay for an RTC.
Also I2C/SMBus is present everywhere on x86, like some graphics cards expose it through their HDMI ports, even some server motherboards have a header for it; but for GPIO I’m unaware of any motherboards that expose it, so good luck researching the chipset and tracing out the pins.