This was an ornament I printed roughly 6 years ago. Being a Christmas ornament it spent most of those 6 years stored in my roof space.
Being in Australia this would have been subject to average temperatures of 30 to 35 degrees c but also peaks across summer approaching 70 degrees c. Also in high humidity.
The PLA crumbles into tiny pieces at the softest touch.
I thought it was interesting that PLA would start to break down in these conditions.
It will decompose, but only it a hot compost pile.
To some extent, this means large scale composting, but you could theoretically do it at home if you live somewhere with four seasons (specifically fall) and have trees that drop leaves on your property or nearby. Let your grass get a bit taller as the trees start turning and mulch/bag the grass and leaf mixture. Bonus points if you have a ratio of 30 carbon (brown stuff) to 1 nitrogen (green stuff) by weight. “Normal” composting into. This is why big piles of fresh mulch get pretty warm and stream in the middle.
I don’t know what it would take to break down PLA in compost, but suspect it would take more time than a typical home pile if you manage to get it hot. It would probably be benefit from shredding to speed things up, as would the rest of the stuff in a typical compost pile. Amusingly, your PLA is probably ripe for getting whacked with a hammer, or a hammer mill.