If you already have a Java system, we stay with it. For a new project with no existing system, we compare with PHP or Node.js, often more economical.
Yes, with modern .NET: on Linux, in containers or in the cloud.
For the vast majority of uses, yes: animations and rendering are smooth. Edge cases are rare and identified during scoping.
Often yes, with a gradual upgrade. If the gap is too large, a targeted rewrite can cost less: the audit will tell.
No: Swift and Objective-C coexist. Migration can be done screen by screen.
It is often due to an outdated target Android version. We update the app and republish it.