The biggest difference is the difference in gate width between the two chips.
The biggest difference between 2nm and 28nm chips is the difference in gate width. nm refers to the process of the chip is also a physical length unit, which is the smallest unit of silicon transistor gate width. The smaller the gate width, the more silicon transistors per unit area, the stronger the chip performance. Of course, in terms of equipment, 2nm is made by euv lithography mechanism, and 28nm is made by duv lithography mechanism.