For most of my life I believed that voting for the lesser evil was the moral course of action. I'm not sure any more. I couldn't, for example, hold my nose and vote for Starmer. I would choke on my own vomit if I tried.
I think the principal is sound but there are limits. I can't vote for a transphobe even if they turned out to be a lesser transphobe than their main rival. And it's not at all clear that Starmer is that given his propensity to say whatever will get him elected.