Hundreds of thousands of documents is small enough that you can feasibly run a pen and paper office handling them. Especially since most of them do not cross-reference eachother (family applications do, but unrelated families have no such links).
That America's brightest tech minds can't solve this problem is embarrassing. (Never mind the baggage of giving a foreign, potentially adversarial nation access to something as sensitive as residency and visa information.)
This article is about the UK.
I assumed that when the GP said the UK was "giving a foreign, potentially adversarial nation access" the GP meant that the US is that "foreign, potentially adversarial nation"
I can't believe that in our timeline Europe has to think like this, but here we are.
I'm well aware.
Note that Palantir is an American company that failed to solve this problem well, and introduces an adversarial risk to the UK.