The UK also has a FPTF voting system, yet the Lib Dems won enough votes in the past to form a coalition, and currently the 5th biggest party in parliament (Reform) is leading the polls, and the 8th biggest (Greens) is often-times polling in 2nd place. Even if you might not win the next election, you can help build something that gets the "only-ever-vote-for-1-of-the-2-leading-horses" people to also vote for it after that.
Some people will never vote for parties that cross ethical lines like genocide, omnicidal climate change, capitalism, oligarchy... For these people the lesser-evil is still way too evil.
“It is infinitely better to vote for freedom and fail than to vote for slavery and succeed.” - Eugene V. Debs, Appeal to Reason, 1900-10-13.
“Wage-labor is but a name; wage-slavery is the fact.” - Eugene V. Debs, The Socialist Party and the Working Class 1904-09-01
Being complicit in making the system more evil is fine for people who vote for the Ds; but if the Ds want the votes of the 41% of people who didn't vote (some because they won't cross ethical lines like voting for a pro-genocide, pro-omnicide, pro-capilatist party), then they need a different argument than "vote for the lesser evil again bro", because that didn't work against W and worked only a third of the time against Turmp. The Ds need to either give better reasons for voting for them, or they need to stop being a pro-genocide, pro-climate cascade, pro-capitalist party.