It would be no surprise for lemmings that the best for the environment would be to reduce consumption, then reuse what you already bought, then recycle (including composting and whatever) what lost usefulness. In this order. Regardless of methane, compostable cups are not the solution - the solution is to not use disposable cups on first place, unless you have a pretty good reason to do it.

This is the best summary I could come up with:

There is a voluntary certification system through the Australian Bioplastics Association, but because the industry isn’t regulated, all sorts of materials are being called “compostable”.

Only South Australia has a statewide system allowing compostable packaging to be put in green FOGO bins.

When organic material such as plant-based packaging breaks down in landfill, it creates emissions of the very powerful greenhouse gas, methane.

Tony Chappel, the CEO of New South Wales’s Environment Protection Agency, says the more inert — or chemically stable — a material is, the safer it is in landfill.

PFAS — or “per- and polyfluoroalkyl substances” — are a group of chemicals used in products ranging from cookware and clothing to cosmetics and food packaging.

Despite “compostable” products meeting the Australian standard for certification, a CSIRO study found their presence in soil meant earthworms and roots did not grow normally.

The original article contains 938 words, the summary contains 139 words. Saved 85%. I’m a bot and I’m open source!

TLDR: Maybe. Compostable bio plastics are better than non biodegradable plastics. Some of these products currently contain PFAS, which is not good, but should be phased out over the next year.

Personal experience with these stupid things is that people put them in both paper and plastic recycling, turning both into trash (you cannot mix trash and recycling)