It's all a part of the crazy Euro5+ emissions regulations. The ECU's are locked on the Storm models -on. Up to 2024 seem OK, I've recently added the Penner map on my '22 GT but a friend of mine in the UK has bought an aftermarket (De-Cat) exhaust for his '25 Storm GT and it has sockets for two o2 sensors (before and after the cat) and that can't be by-passed because a) the ecu is locked, and b) if it detects any variance outside acceptable parameters between the two sensors - the engine won't start.
The purpose of all this lot is to ensure the emissions remain as per the factory settings for the life of the bike ! I assume the US Storm models have only one o2 sensor (not being subject to the euro nonsense) ?