ok… the default seems to work as expected.
this is my configuration for the item:
Group Thermostat_Arbeitszimmer "Thermostat Arbeitszimmer"
(Arbeitszimmer)
["RadiatorControl", "Thermostat"]
Number:Temperature Thermostat_Arbeitszimmer_Setpoint "Thermostat Arbeitszimmer Soll [%.1f °C]" <heating>
(Thermostat_Arbeitszimmer, Thermostate)
["Setpoint", "Temperature", "TargetTemperature"]
{ channel="zigbee:device:controller:00158d0000000000:00158D0000000000_1_thermostatoccupiedheating",
widget="oh-stepper-card",
listWidget="oh-stepper-item"
}