The problem is sadly a bit more complicated. Thanks to the winner takes all system over in america a third party candidate has virtually no chance of being elected. Therefore if you want to counter a candidate you disagree with you have to necessarily vote for the most popular candidate that you can mildly agree with.

Some states have signed a pact to switch to ranked choice voting (i think new york and new hampshire are among them) which will help a lot with this problem on a state level. Only when most states adopt this it will matter on a national level.

Then and only then will it be viable to vote third party.