Can OpenMQTTGateway be the broker?

I have a Shelly smart switch with Tasmota on it outside the range of my Wifi. I do have LoRaWAN there, so I’m looking for a device that can act as an access point and MQTT broker so that Tasmota can connect to it and then forward the data over LoRa.

Can OpenMQTTGateway do that?

since v1.8.0 - yes

look into the MQTT_BROKER_MODE flag