I don't really see how the Uncommitted movement could have done anything differently. They had pretty simple demands: let a Palestinian speak at the DNC, meet with families of Palestinians, meet with our leadership. The Harris campaign ignored all of those requests, so in the end, they declined to endorse her, but still urged their supporters not to vote Trump or third-party.
Endorsing her just wasn't an option, given that she did nothing to meet them halfway. If your spouse is abusive, and you say, "If you ever treat me like that again, I will leave you," then you have to leave them if their behavior doesn't change. Otherwise, you are just inviting more abuse. If you tell a politician, "These are the minimum actions you must take to earn our endorsement," and they ignore you, you can't endorse them anyway. Otherwise, you're announcing your demands carry no weight.
The Abandon Harris (previously Abandon Biden) movement was more hard-line, and the Democrats were clearly too centrist and hawkish to meet their demands for an immediate arms embargo But the Uncommitted movement offered reasonable steps that the Harris campaign could have taken to win over Arab Americans, and she flat out ignored them. She is clearly to blame for not taking that offramp.