[schroeding]

I just took a picture of every Euro banknote (which of course have EURion on them) in my wallet with my Poco Phone (which has the same MIUI version / camera app) and all photos are perfectly normal

But could of course be a special change in this Xiaomi model :-)

The german postal voting documents do, with 99,9% certainty, not include any EURion constellations (---and they have no window, the return address is printed directly on the envelope--- EDIT: they do in cologne! See [1], last image, sorry for the misinformation). Wouldn't make much sense, as the envelope is thrown away immediately and the inner letter (which is not the ballot) contains a unique number per postally voting citizen that's not trivialy guessable.

They are however made from non-bleached (only coloured) recycling paper, so maybe the camera is picking up some artifacts from the different visible paper fibers?

[1] https://imgur.com/a/SCHGo4N