Believe it or not, policies aren't as important these days as what people believe you generally stand for and against. This is shown regularly when Labour or Tory voters are asked about manifesto's at election time and regularly agree with the oppositions manifesto if they are deceived into believing it is their own parties.
Labour need to address that.
Policies are useful indicators and the 2017 manifesto was an exercise in compromise within the party and restraint on behalf of the Corbynites, so people saw the Party was not going as extreme as feared.
But 2017-2019 saw Labour confusing the public on Brexit because it's leader, amazingly, had no interest in Brexit and couldn't be bothered to take a position, the members and voters wanted a confirmatory referendum, but Corbyn's tiny influential inner circle wanted full on Brexit because they somehow thought they would get a Left wing Brexit even though the Tories were in power and setting the agenda. That inner circle took it upon themselves, with their proximity to Corbyn and influence and authority derived from that, to take advantage of the vacuum
What we ended up standing for, in the minds of the public, was excusing russian poisonings on our soil, bullying and tolerance of Weinsteinlike inappropriate advances towards female staffers and of course anti-semitism.
Starmers 'principles' are good, we just need to push that narrative rather than pick it apart on the details and undermine it from within. We need to look electable, not do a better job for the Tories than they can manage themselves.
A couple of flagship policies to illustrate a broader direction is all that is required.