Sinwar did not accept it, so no, Hamas officially did not accept it. While members of Hamas had taken it favorably, he did not, and that's what counts.

The resolution itself says Israel accepted it.

https://en.wikipedia.org/wiki/United_Nations_Security_Council_Resolution_2735?wprov=sfla1

The resolution, presented by the United States, details the three-phase proposal and notes Israel's acceptance thereof.

While initially Netanyahu grumbled, Israel accepted it.

https://www.state.gov/briefings/department-press-briefing-june-24-2024/

QUESTION: Yeah. Sorry – (laughter) – I have so many. Yesterday, the prime minister – the Israeli prime minister – basically rejected the whole Biden plan, and he said, okay, we want to exchange some of the hostages for a few prisoners and that’s it, that’s the end of it. So do you still think that the ball is in Hamas’s court and not in Israel’s court?

MR MILLER: So I saw the comments the prime minister made yesterday, and then I saw the statement his office put out clarifying that they wanted to secure the release of all hostages, and then I saw the further statement the prime minister said today where he said – made clear he supports the proposal that Israel put on the table and the President laid out. So I will just say I think all of us that speak publicly at times make mistakes and misspeak, and when we do so, we have an obligation to come clarify. And we’re glad he did.

While members of Hamas had accepted the proposal, and after bad faith negotiations from Hamas, the one guy who actually had the power to accept it did not. Netanyahu's fear of losing power aside, had Hamas actually accepted the proposal, this would have panned out better. It would force Netanyahu to rebuff the acceptance of the proposal without being able to say Hamas made unworkable demands.

https://en.wikipedia.org/wiki/Three-phase_Israel%E2%80%93Hamas_war_ceasefire_proposal

On 10 June, the UN Security Council adopted Resolution 2735 backing the 31 May proposal, noting Israel's acceptance thereof and calling on Hamas to accept the proposed agreement as well. The following day, Hamas and Islamic Jihad replied to the resolution with amendments to the proposal, including a timeline for a permanent ceasefire and troop withdrawals, and the Office of the Israeli Prime Minister stated, "The claim that Israel agreed to end the war before achieving all its goals is a total lie". The United States responded to the Palestinians' proposed amendments by calling them unworkable. The day after that, Hamas denied adding any new ideas to the ceasefire proposal. On 21 June, Hamas stated, "The priority is to stop the criminal war on our people", and three days later, Netanyahu stated Israel would only accept a partial ceasefire that would not end the war.

...

October 2024, U.S. officials said that they believed that Sinwar was no longer interested in a ceasefire deal with Israel. These officials said that Sinwar had become "inflexible" and "fatalistic" as the war had progressed, adding that he was hoping for it to expand into a wider regional conflict involving Iran.

https://www.state.gov/briefings/department-press-briefing-october-17-2024/

So, a few things about that. First of all, as you know, we’ve been trying to achieve a ceasefire that returns the hostages home, alleviates the suffering of the Palestinian people, and ends the war for many months now. And the chief obstacle to reaching that ceasefire and bringing an end to the war has been Sinwar, who has refused to negotiate at all in recent weeks and has said no time and time again. That obstacle has obviously been removed. Can’t predict that that means that whoever replaces Hamas[1] will agree to a ceasefire, but it does remove what has been in recent months the chief obstacle to getting one. So,we’re going to continue to work with our partners to try to find an end to the war. The Secretary already today while on Air Force One with the President flying to Berlin called the prime minister of Qatar, who has been one of our two mediators – other mediators – working to reach an end to the war. He called the foreign minister of Saudi Arabia to talk about the path forward, and he will be having additional contacts in the days ahead.

https://www.state.gov/briefings/department-press-briefing-august-7-2024/

MR MILLER: I don’t think there is. I really don’t think – it’s what the Secretary said yesterday, obviously, and I think is accurate, which is it doesn’t really change the situation. Two things can be true: Number one, Sinwar is a brutal terrorist with blood on his hands, including the blood of American citizens, and not just American citizens but citizens of many countries around the world. Let’s remember, it’s not just citizens of Israel that were killed on October 7th; there were citizens of multiple countries, as I said, including the United States. That is true.

It is also true that he continues to be the person that calls the shots for Hamas. And that was true before the death of the leader of the – the political leader of Hamas; it continues to be true today. Ultimately, it was Sinwar that had the final decision-making authority, as we can see throughout these negotiations, on whether to accept a ceasefire or not.

So yes, Sinwar absolutely ought to be brought to justice. We believe that, for the – his significant acts of terrorism. And we also think he ought to accept the ceasefire deal that is manifestly in the interests of the Palestinian people as well as, of course, in the interests of Israel and the broader region.