Is a cardinal allowed to vote for himself to be the next Pope? NT

There’s currently no rule against cardinals voting for themselves (since it’s a secret ballot). But in the past (from 1621-1495), the method of voting used was designed to prevent voting for yourself.

From Wikipedia:

So there is now a secret ballot, but a 2/3 majority is required. So you can vote for yourself and perhaps be the vote that tips it over the 2/3 cutoff, but that means that nearly 2/3 of the cardinals voted for you anyways.