In hindsight, Corbyn should have known how to do this right
He's seen the splitting of the left over past decades on everything from trans to war to immigration. He's also seen the splitting of the entire society on a few dozen different issues, from AI to Climate to Viruses.
"Your Party" was the perfect name for a party which could have "nutmegged" all other parties by appealing to almost everyone, and having zero in-fighting at the same time.
How? Campaign for grassroots democracy, where debate and decisions on the contentious issues are overwhelmingly at the local level. If you don't like the way your local democracy is going, just move down the road where the voting is more along your lines.
No need to have a platform with anything more than that. If you don't agree with it, join a party that only wants to appeal to half of the population at the most.
Now, if there is no work needed to create party policy, what work can be done?
Simply outline the contentious issues, and explain all the ways they could be addressed at a very local level, while bringing all walks of life closer together.
Formulate ways to make local debate as seamless as possible. Work on deepening democracy and finding the best compromises for all the issues.