Do universities still, as some did in the past, sing
”gaudeamus igitur” at graduation ceremonies?  Is/was it sung in the US?

Wikipedia:

The song dates to the early 18th century, based on a Latin manuscript from 1287.[1] It is in the tradition of carpe diem ("seize the day"), with its exhortations to enjoy life.

It was known as a beer-drinking song in many ancient universities,

It was once sung at American universities in days past, and it is probably still performed at some graduations, but most people wouldn’t know it to hear it.

I’m only aware of it from Tom Lehrer’s song Bright College Days, which contains the lines:

Turn on the spigot,
Pour the beer and swig it,
And gaudeamus igit-ur.

You can hear it in Brahms’s “Academic Festival” Overture.

A few years ago there appeared a Listener crossword puzzle that required a knowledge of the opening lines as its last step. The crossword fraternity was sharply divided into those who appreciated it and those who believed that requiring a knowledge of Latin was unfair.

It’s sad, really. Classics is associated in the popular mind with crossword puzzles, as when the uncircumcised philistines mock the study of it as being only useful for solving the Times crossword (it’s always the Times, for some reason). And many of the earlier setters, and undoubtedly the solvers, had classical backgrounds. But nowadays, at least as far as cryptic puzzles go, you’d probably find more maths and computer types, and a standard cryptic clue is more likely to be an equation of the type A +/- B = C than to require knowledge of either classical languages or history.