multi-sim - which data plan will it use?

If I have a iPhone 11 where 1 sim is a UK plan and the e-sim is US (AT&T) plan, does it use both data plans simultaneously? e.g. if i'm in the UK, I do not want my phone to use the AT&T data but still would want to make and receive calls via it. vice versa, if in the US, I would not want my UK data plan to be used.

is it clever enough or do I have to manually change settings every time I travel?