Hi @Bastro0107 welcome to the community and thanks for posting!
As you alluded to, the thermostat controls are typically disabled when the system can’t determine if you would be attempting to adjust the heating setpoint or cooling setpoint.
Is the thermostat currently reporting the Mode as ‘Custom’? Since the thermostat seems to be a Heating Only thermostat, we would normally be able to infer that a heating adjustment is desired even in ‘Auto’ mode, but I suspect that if the mode being is reporting as ‘Custom’ it could be throwing things off (as it’s not an officially supported Thermostat Mode in SmartThings).