The official compatibility list is short because it only includes devices that have actually been tested by SmartThings. Here’s the UK list:
https://www.smartthings.com/uk/products
Beyond that, see the following FAQ (this is a clickable link)
While zigbee is the same frequency worldwide, there are actually many zigbee devices that won’t work with SmartThings, and a number of US zigbee devices which would be illegal to operate in the UK because the US allows for higher power transmission levels. But see the FAQ above, it will explain further.