OK, so as you can see from the table, that version does indeed use docker. It also supports Add-ons which explains why you were able to install the Zigbee2MQTT Add-On (which you would not be able to do if you had installed the Container or Core types).
Is it fair to say that everything you have that is ZigBee based is working except for the Tradfri Remote? Or is the problem more widespread?
If it’s only the Tradfri Remote, you may wish to consider installing ControllerX. It’s specially designed to make remote-controls easier to use in Home Assistant.