Plurality voting only really works well in two candidate elections. In three candidate elections, you start to frequently run into problems with spoilers.
Because of that, the best performing third parties in countries that use plurality are regional ones. You’ll have local elections where one of the national major parties is functionally a third party.
Trying to oppose the two party system by just voting third party is about as effective as trying to end car dependency by just biking down major stroads. Without changing the underlying environment (e.g. switching to a better voting system or building a protected bike lane), most people won’t follow you.