Not quite on the level of others mentioned, but Freilassing on the Salzburg-Munich line was quite grim and seemed a shadow of what it was
Plus the unsightly steel sheeting that was erected during the immigrant crisis of 2016, to keep prying eyes away from the border checks.
I was the only passenger to board an EC train at Zebrzydowice on the PL/CZ border a few years ago, a big barn of a place with no purpose today.
Having said that, EU states maintain emergency powers to check passengers, and did so in places during migration peaks and Covid, so the railway can't just demolish those facilities.
Away from Schengen, there are also checks today where once there were none, eg at Dobova* (SI/HR) and at Tovarnik/Šid (HR/RS).
The latter border has all the signs of a pair of wayside stations suddenly catapulted into the status of major border posts with all the associated bureaucracy.
Przemysl (PL/UA) is another former sleepy border town which has become a major focus for emigrants/refugees from Ukraine, although the actual border posts are some 15km to the east.
Then of course we have the UK, with EU passport stamps, longer immigration queues and reduced Eurostar capacity, soon to be further complicated by the introduction of automated EES and ETIAS systems.
* Croatia is about to join the Schengen zone, so maybe this check will disappear soon.