My personal idea would be to have a party that runs on systematic reform while avoiding any of the touchy political questions like gender politics or something of the like. Basically a generic 'fuck off' party that is an actual systematic fuck off.
Americans , by now, have zero trust into their system. A party capitalizing on that that just vows to create a better and fairer system in the very abstract procedural sense could speak to a lot of current nonvoters and both parties alike and would benefit every time the trust into the current system diminishes.
It would have a far better selling point to vote them than the green or libertarian party.
Well, that's one way to stay irrelevant and not gain any traction. Tons of people acknowledge systematic reform and social reform as going hand in hand, and I assume it's the right who don't. But if you don't endorse white supremacy or cracking down on people of color/immigrants, then you won't win over their votes either compared to the Republican politicians who promise either of those.
By not addressing social issues like gender politics and racial issues, you keep the trust at zero, and you offer NO reason whatsoever for majority to even think of your third party. You can't create a better and fairer system without addressing gender issues, racial issues, LGBT+ issues, and whatnot.
For example, if you talk about infrastructure, you might also have to talk about prioritizing locations. Where would you prioritize fixing, upgrading, or adding new infrastructure? Affluent areas or poor areas that desperately need better infrastructure, especially when it could help them economically?
Social, economical, and political reforms are all tied to each other.