It is possible, but a major US election requires a massive burst of popularity to avoid splitting the vote of the majority candidate having "less shitty than the other guy" policy positions. Failure to breach that threshold hands the victory to the majority candidate with the shittiest position on policies.
The simple test is this: has your third-party candidate achieved a realistically high margin of popular opinion behind them? I'm not saying be a slave to polling, but it isn't rocket science either. You will know if a third-party candidate has momentum behind them. They have charisma that sucks people in. They are somehow getting attention regularly driven to them despite the majority candidates pumping much more money into the news media.
If the third-party candidate doesn't have something bordering on a revolutionary ideological movement backing them, they aren't going to make that cut in a nationwide race.
Edit: I'm not saying give up. Donate to causes you honestly believe in. Volunteer. Do what you can to make a difference. Support local government efforts to implement ranked choice voting in your state, which can and will break this system. (look at Alaska) But when it comes to casting that final vote, be realistic, even if it means voting against all the hard work you just put in. Sunk cost fallacy at the expense of giving away victory doesn't help anyone.