Create a 2.x version leveraging commerce_api (JSON:API)

Thanks @mglaman I just thought the same :)

Until that it might make sense to add information on the module page linking to this issue and pointing out that JSON:API + commerce_api is preferred (but not yet supported) over https://www.drupal.org/project/commerce_cart_api →

I just needed some hours to find out if it's better to use REST or JSON:API with Drupal Commerce. => JSON:API seems to be the better choice but is incompatible with this module.

An alternative to a 2.x version might be a separate project like commerce_api_cart_flyout or something like that, which shows the hierarchy?

I think a 2.x would be best. Commerce Cart API isn't the "standard", whereas Commerce API is. So 2.x would reflect decisions made. There could be the problem where 2.x also replaces Backbone/Underscore with web components and Commerce API. Those are two big changes. But maybe that's just the way it has to go.

Okay thank you @mglaman :)