"...Negotiations on an agreement had stretched for more than two years, leading Biden to appoint an emergency board in July to help break the impasse."...
That's what real "Leaders" do...understand the problem and make the necessary adjustments (i.e. creating an Emergency Board), and empower them to get a resolution...Biden is the 'Chief Executive'...it is bad management for him to spend all his time doing the requisite negotiating required for this deal...there's still other issues...like Ukraine...to attend to.
I have little doubt that after creating that Emergency Board, the issue was brought up multiple times in his briefings and ultimately required his approval...so yes, Biden 'Brokered' this deal.
Link: https://gcaptain.com/biden-brokers-deal-averting-nationwide-rail-strike/