literally everything, with infinite time to spare. (this is another reason why immortality sucks cock, btw)

Better use of immortality:
Live different lives every so often. Different perspectives, experiences, and a fresh start with fresh discoveries.

Knowing everything gets boring after awhile, after all.

Unlike what borges says, you won't experience everything even with unlimited time.

Let's make an absurd example: you may not ever shake hands with a person which
1) is not your son
2) is named Steve

This because it depends on external factors.
For instance, if you are given infinite time rn, you'll never be able to be buddy with [elon musk, Steve jobs, bill gates, etc] in uni.

So technically you cannot do anything.