At scale the US system has too many layers of abstraction. We are not a direct democracy once you pass the small scale elections you mentioned. Those abstractions combined with first around the goalpost winning makes it so statistically the chance of third party success rounds to 0. So if you vote 3rd party in a major election when you otherwise would have voted Biden then you helped Trump because that 3rd party vote's only impact on the election was to reduce Biden's total by 1.

The only chance 3rd party has of gaining ground is if we switched to ranked choice voting as this would allow people to realistically gauge and react to support for 3rd parties without aiding the major party they dislike in the meantime.

Also need to ditch the Electoral College as it is the worst of our voting abstractions that is only amplified by gerrymandering.

And based on this list, some small parties actually have some seats and even have some mayors somewhere. So it seems like the vote is not 100% wasted.

On the national level, it's wasted. Essentially, the system used in the USA is called First Past The Post - the majority (or plurality) winner of the vote gets the office. No proportional representation. That means when there are two parties which are near clinching a majority (as in almost all national races here in the US), votes for a third party are wasted.

You are not wrong, but missing essential context. The American electoral system more or less ensures there can never be more than 2 competitive parties in any given election.

In some cases where republicans are not competitive, voting third party may be a reasonable strategy, but this is usually only the case in local races in very partisan districts.

If you want multiparty democracy (which I agree would be an improvement), it’s far more important to advocate for electoral reforms that would allow such a thing than to actually vote for third parties. To do so actually gives up your influence and can be an act of self-sabotage, even if your goal is to support third parties.

Political illiteracy accusations from someone who thinks that Trump didn't try to stage an autocoup? Bold move.

Well, that's always been the case. But it is still an important step when there are only two candidates on the ballot, and one will severely damage left causes.