We need platforms to offer that interoperability and simply connect to these “marketplaces.” Take Shopify for example, sellers use that platform to list on Amazon, Google Shopping, TikTok shop, etc. We need open source alternatives to those where the sellers own the platform and these marketplaces are forced to be interoperable or left behind by those that are.
For Facebook, Instagram, Twitter, each person having their own website where they post and that post being pushed to these platforms is also another way to force interoperability on them or be left behind.
It’s a tall task, but achievable and it will happen given enough time.