Fixing all of those at once might be a bit too much to ask, but I have some quick suggestions. I'd say for a more robust JSON you could try Dhall. If you just want to exchange lumps of data between programs I'd use Protobuf. If you want simple and freeform I'd go with good old sexps.

https://github.com/dhall-lang/dhall-lang

https://protobuf.dev/

https://en.wikipedia.org/wiki/S-expression

Suggesting protobuf as alternative to JSON is crazy talk.

And this is why I was asking the question in the first place.

Not that I'm a fan of JSON, but I fail to conceive anything better as a general purpose protocol.

You must not have seen the abject misuses of JSON I've seen then