Is it possible to build multiplatform project, so it compiles to jar and js, where js will be run on iOS and loaded during runtime. Goal would be to update part of ios app without pushing new version to appstore. No dependent libs except kotlin itself. Maybe there is already example?

Yes

There was a react native based startup that did this as a service. Apple found out about it and suspended all apps that were using that framework. Generally, downloading code is against the App store rules. Your app isn't supposed to change after it has been reviewed. If your app is a game there is some allowances for downloading code. They also don't care as much if you are doing a/b testing. What are you trying to accomplish besides not going through the app review process for every change?

Our code "interact" with physical objects manufactured by 3rd parties. Once in a while, new type of objects created, and we need to add support for them in our app (which include some static data and new or changed algorithms). Without support it is very inconvenient for users to interact with them. Now users have to wait for new version, which may take few month, while writing code and testing it is just few hours.

That doesn't appear to be a significant change in functionality. You would probably be safe though I would try to make the app code as robust as possible to avoid having to live update code. Just FYI, app review times are typically 1-2 days. New apps and major version changes seem to take that full amount every time. I can say that I've had bug fixes submitted in the morning and released later that afternoon but I wouldn't count on it being like that every time.