Yeah, people forget that form follows function.

The parameters for making a USEFUL plastic that ALSO degrades gives a narrow band. Too degradable, and the function of fulfilling all the areas plastic is currently used for can't happen. Not degradable, and we have the current situation.

Plastic being is in use not simply to fuck the planet over or something, but because compared to other materials it has physical qualities that things like glass, wood, fabric, etc. don't have, that's why it's ended up in so many things. It's lightweight, strong, and "plastic" (that is to say, more easily shaped and molded than other materials, and I suspect there's a labor component too where maybe it needs less labor to shape and form).

I'm eventually going to write a story about a sci-fi world that's under quarantine because they successfully made a plastic-eating bacteria that never stops eating and breaking down plastic. Go there and most of your technology/clothes/etc. are eaten away. I might throw in wood, too...a world with no wood or plastic because the local bacteria is like, "Yum, yum, food!" and gets into every nook and cranny. I anticipate I'll have to do a lot of thinking to figure out how drastically technology would change under these parameters...I imagine a lot of it would be very "brutalist" because you'd have to rely on heavy-as-balls metals and cement and stone and such. Unless there's an Aluminum Future or something, where everything that can be made out of aluminum, can. Of course, there's also the byproducts of intense metals mining to think about on a fictional world like that. Anyway, lots of details to pick apart for worldbuilding.