Like a giant garbage disposal of dolphins?

There ARE bacteria that can digest certain plastics.

"plastic" is just a catch-all term for polymers, but there are different kinds made of different materials. Your phone case isn't the same plastic as a milk jug. (abs/PETG vs HDPE, their long science names don't really matter it's just to show the difference)

Over the decades, certain kinds of bacteria have been shown to eat certain plastics in the right conditions.

Unfortunately, it's those "right conditions" that make large scale plastic disposal via bacteria not feasible right now.

I'm sure someone is barreling toward discovering a "this thing eats almost all polymers in normal outside temperatures" to make their company more profitable, while ignoring the fact that if it breaks out of their containment areas, "bacteria that can eat all your plastic things in a few weeks breaks containment, billions in damages already" could potentially hit the headlines within a month.

Yeah, that's DoOmPoStInG but it's a potential thing that could happen, and people are actively TRYING to make some of those things happen already, so it's within possibility.

Im always doing a bit

It's not outside the realm of possibility. Though it had to be the perfect storm for something like that to cause a global catastrophe.