Pennsylvania

There's nothing illegal or wrong about leaving some spaces on a ballot blank. By law, all ballots are to be counted whether or not they're completed.
Voters often don't feel sufficiently informed about a candidate, a race, or a referendum issue, and would rather leave those portions of a ballot empty instead of casting an uninformed vote.

While it's fine to abstain from voting or leave blanks on a ballot because you feel you lack knowledge, experts recommend that you do what you can to fill out an entire ballot. At the very least, they say, you should make a special effort to vote in the races and ballot issues that are likely to affect you directly: state legislature, city council, school board, and referendums that will impact where you live.

https://www.findlaw.com/voting/my-voting-guide/can-i-leave-blanks-on-a-voting-ballot.html