This is laughable. Russia cannot give any credible security guarantee to a country that it has just invaded! The war has shown precisely that Russia still believes that it has the right to control Ukraine and that any negotiated peace is nothing more than a temporary pause in hostilities in anticipation of a more opportune moment for Russia. Putin is a cypher and no-one really knows exactly why he wants to invade and conquer Ukraine, but as it is enormously plain at this point that he does want to do so, this entails that there is no really workable negotiated settlement.
Security guarantees would be provided by Western countries, not only Russia.
Russia's key conditions for the supposed "deal" that you refer to were that (i) the size of the Ukrainian army would be heavily constrained and that (ii) Russia would have a veto on any response to future aggression against Ukraine. Ukraine rejected the deal because it would have been worthless.
That Russia and Ukraine were negotiating an end to the war, early on, and that their representatives met in Istanbul and hammered out a deal is not in dispute, you can find information about those talks all over the 'net, e.g. here by the BBC:
https://www.bbc.com/news/live/world-europe-60890199
And here by Reuters:
https://www.reuters.com/world/europe/turkey-says-russia-ukra...
From what I can find online, the negotiations advanced to the point where there was a comprehensive deal on the table that detailed security guarantees for Ukraine and a neutrality commitment on their side, but the deal was abandoned. Mearsheimer has claimed that it was because the US and the UK told the Ukrainians to drop the deal because they could win the war with the continued support of the West (and we saw how well that turned out). I obviously don't know enough to tell for sure whether that claim makes sense. There may well have been more than one reason that the deal fell apart.
Details here:
https://archive.ph/ajonZ
And a longer discussion here, were a speaker claims that Putin's plan was a US-style change of government, like the Americans did in Baghdad, (and we all saw how well that one turned out):
https://www.nprillinois.org/2024-05-06/the-story-behind-2022...
I don't know who those people are though in the panel, so I have no idea about their credibility etc.
Now, whatever the reason for the negotiations, I think it's indisputable at this point that Russia did come to the negotiating table and proposed terms to end the conflict. A sensible thing to do given that their "special operation" was, at the time, going to the dogs.