Question about Garmin City Navigator NT

I had bought the Garmin Nüvi 52 LM in 2014 in the US as it was cheaper than renting one for the rental car.
With this upgrade (to SMC map) I wanted to expand it to Europe.
After a few hours of practicing around I abandoned the experiment. It does recognise the chip but cannot load the detailed map. But I can't say definitively whether it's me or the compatibility. Maybe the US version only works with US maps.

In the meantime I have downloaded HERE Maps onto my iPhone. They also work offline and I can use them as a pedestrian. I no longer need an extra navigation system. I would not invest more money in a dedicated navi.
The upgrade comes with no usable documentation. I tried to read up on it in Youtube videos.