Kid, your sheer ignorance is staggering; with the world in absolute chaos thanks to the USA and Israel starting an illegal war they cannot win, Starmer has better things to do than worry about assisted dying.
Also you simply don’t understand how Parliament works. There is absolutely no chance of an Assisted Dying Bill being in the next Labour manifesto. What it might do is to allow Parliament to decide. In the former case (which won’t happen) Labour MP’s would have to vote in favour; in the latter case it would be a free vote (no 3 line whip).
In the latter case, Starmer would not be supporting it, but merely allowing all MP’s to have their say. I hope you understand the difference which is critical.