I have great hot water pressure. It's the cold water in one end of mobilehome. Not just shower. The sink also.

I am not an expert but maybe it is the point where the supply is connected. Is that closer or farther from where the pressure is low? Has it been that way or just started doing that? Also check if something is leaking or running like the toilet tank.
Hope this helps you find the problem.

How old is the mobile? Do you know what type of water lines it has? Many older trailer homes had galvanized water lines, which are prone to plugging over the years.