I think voting third party is viable when it comes to local elections/electing Congress people and senators. When it comes to the president, it is much much less viable. If you want a third party president to be viable, you must first build up that third party's power and at the same try to prevent a fascist takeover so that third party power buildup can be sustained. Building up the power of a third party takes decades of work. Further third party power can be amassed through implementation of ranked choice voting, which takes time to implement as you need to get multiple states to agree to it first.