Edit: Check this out. I found a document from the Texas 2016 race, and the electors were mainly for Trump, but Hillary isn't the only other name they could vote for.
"FOR PRESIDENT: DONALD J. TRUMP received 36 votes, RON PAUL received 1 vote, JOHN
KASICH received 1 vote and no votes were cast for any other person for President of the United States.
No elector voted for Hillary in Texas. But Ron Paul and Kasich were voted for.
https://www.archives.gov/files/electoral-college/2016/vote-texas.pdf
They aren't overturned, as I understand it. They call them "unfaithful electors" and some states have laws against that. Hillary, when she lost in 2016, wanted electors to be unfaithful. The thing is, the electors involved knew what she was up to, and voted for Trump anyway. One didn't. if I remember, but I would have to look it up to find out what the reasoning was. There was at least one elector who was insulted that Hillary had one elector change the vote to her, so he changed to Trump just to show this was an honorable thing to do.