Biden intends to reanimate the Paris process and much else, likely committing the US to a zero net emissions goal by 2050, while focusing on more aggressive 2030 targets, not just for the US, but by compelling other emitters towards more serious 2030 goals.
not just..., but... =  not only..., but also.... 相当于一对并列连词，连接两个介词短语：for..., by....
not just for the US, but by compelling = not only for the US, but also by compelling...

用逗号隔开很正常。逗号其中的一个作用是，表示停顿。