This works because almost all the US uses first-past-the-post elections for the Presidential general election. So you get outcomes like this:
Scenario 1:
Biden: 10 votes
Trump: 9 votes
Kennedy/Stein/West: 0 votes
Biden wins the state
Scenario 2:
Biden: 9 votes
Trump: 9 votes
Kennedy/Stein/West: 1 vote
Tied vote, decided by game of chance/lawsuit
Scenario 3:
Biden: 8 votes
Trump: 9 votes
Kennedy/Stein/West: 2 votes
Trump wins the state
This is why you see huge financial support from Republican billionaires for third party candidates who have no chance of winning.
Not saying you are saying this, but it’s as good a post as any on which to say it:
You can’t dismantle the 2 party system by voting for a third party. Even in the extremely unlikely situation that that third party wins, it will just quickly, if not immediately, go back to a two party system. It’s the nature of a FPTP voting system.
It’s a process you have to start from the ground up. You can’t just vote for a POTUS and then magically we have multiple parties. You have to focus on your local politics and get people into office who will push to get our voting system changed. And that will have to “trickle up.” It’s not something that will be solved overnight, and people focus too much on the POTUS, when they should be putting their effort in where they have the most influence: locally.