"In a 2023 blog post, external, Palantir described the challenge of combining data from multiple government systems containing tens of thousands of visa applications and hundreds of thousands of accommodation offers."
This is the kind of thing GDS and other Civil Service departments build all the time, its a completely standard kind of challenge that a small team of Devs (+ supporting staff) from a departments DDAT department does day in and day out.
The output will be open source by default and use existing standards.
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.)
Could probably be moderately complex excel sheet. Well, hopefully not but keeping that one guy that know how it works is still cheaper than Palantir!