One can go mad staring into the minds of genuine swing voters, but importantly they aren't "the center" as defined by DC centrism, but rather weirdos with an odd mix of policy preferences, if they have policy preferences. It's possible for them to vote for Democrats for, I dunno, weed legalization, and then vote for Republicans next time if they don't get the weed legalization because if they can't have that then they hope to see more immigrants in concentration camps.
My point is, while most people are fairly well sorted into the two parties at this point, the remaining weirdos aren't necessarily completely irrational. Just a different priority mix.
Probably the best way to appeal to them, as block, is actually just vibes.