I've not tracked this closely. I thought Trump's position has been that the prospective Moscow deal had run out of steam in 2015. The Democrats have been trying to argue that Trump was still active in trying to make the deal well into the primary season in 2016, during the period in which they accuse him of sucking up to Putin and collaborating with the Russians to hack the election. From the current Buzzfeed story, it seems Cohen is supporting the story that the negotiations were still live in 2016. Even if true, however, that wouldn't answer the question of whether those talks were serious or perfunctory, or whether Trump was significantly involved.
Trump was no longer exercising day to day operational control of the business by that point but he would presumably have gotten periodic status reports which are potentially subject to malign characterization by his critics. Don Jr, Ivanka, and Jared, however, were operationally involved in the company. How deeply Trump relied on them during the campaign, I don't know, but he brought Ivanka and Jared into the White House, which opens another avenue of complication. Many here -- including the amen corner who want to regard DJT as the sublimely brilliant Jedi master playing n-dimensional chess and toying with the mere mortals in the opposition -- yeah, even them -- tended to agree that it was reckless and improper to ignore the nepotism rules and bring immediate family members who are running the business into government.
The Buzzfeed "revelation" is that Cohen did that alleged lying in 2017 because Trump told him to. So there are at least two questions, was it a lie (or did he lie about lying) and was he directed to lie.