Just my personal opinion - please be not discouraged:
openHAB it’s great, but not the best option for HomeKit integration
if you want to use openHABs capabilities and want to use HomeKit as User Interface than openHAB + Homebridge with the steilerDev/homebridge-openhab2-complete works quite well (also compatible with openHAB 3)
if you are only interested in making your devices available via HomeKit than you might skip openHAB completely and check if Homebridge fulfills your needs
the native openHAB HomeKit Binding was, the last few times I tried it, simply not very reliable…
The thermostats do not have different modes, they just have current and target temperature. I followed your advice in this Post (Homekit thermostats | Remove unneeded modes) and set up two string items for current and target mode.
If I understand correctly, this command will set the respective variable “workTargetThermostatMode” to “AUTO” and it therefore can be forwarded to HomeKit.
I will try this with my two variables and see how far I can get! Thank you, Eugen!