The immediate fix to this is regulatory action. Facebook has made itself indispensable in a number of areas that are in the public interest and should be treated as a public good for these purposes. Ads are pollution, and Facebook is forcing people to choose between ingesting pollution and using facebook marketplace, or throwing their used but functional goods in the garbage.
the immediate fix to this is to stop using facebook. If your local government are using it to publish whatever useful infromation, it may be possible to sue them on the grounds that publishing their public 'good' on a private platform exclusively is against some kind of public records law. Alternatively, eventually they will publish where the audience is, if the audience is not on facebook then they will publish some…
Sure, but that relegates my old but perfectly functional macbook to the trash. There's literally no functional alternative to fb marketplace for getting used goods re-used at any kind of scale.