There are a couple of different LoRa types: plain LoRa, and LoRaWAN, and the HA Community uses both kinds.
I myself have only used plain LoRa for my DIY projects. I use OpenMQTT Gateway to receive LoRa signals from the remote Sensors and the MQTT part works with HA. You should be able to find on the OpenMQTTGateway site a compatible LoRa receiver that runs OpenMQTTGateway software. Also check that the receiver can be bought for U.K. frequencies which I understand would be 868MHz (maybe 433MHz as well) but double check to be sure.
As for your particular application, here is a LoRa mailbox sensor, that has a version with magnetic contact closures that I would think you could use for a gate open/close sensor. I have used his original mailbox sensor that was based on a motion sensor, but have not used his more recent versions, but I think they should work for you. You should be able to set the power level to around +20dBm to get much better distance than ZigBee.
Here are a couple of other references you can use to research further: