I think its inevitable that something (either from humans or nature) will figure out how to digest plastic. Similar to the Devonian Wood Crisis.

Bacteria and fungi are like, "Hold my beer...":

Bacteria: https://microbenotes.com/ideonella-sakaiensis-plastic-eating...

Fungi: https://www.colorado.edu/ecenter/2021/11/04/plastic-eating-m...

It's unfortunate that the mushrooms grown on plastic waste absorb chemicals that make them unsafe to eat. What a gamechanger otherwise.

From the linked article:

"The oyster mushroom is capable of decomposing plastic while still creating an edible mushroom. This opens up doors for its use as an at-home recycling system."

Sure, but in evolutionary timescales a hundred years of selective pressure from newly abundant plastic waste might produce an organism optimized to exploit the niche from human landfills and ocean trash in a breezy 20 million or so years.