A commercial Vaadin subscription is required to use Multiplatform Runtime in your project.
Multiplatform Runtime (MPR) makes it possible to run applications and components written with Vaadin 7/8 inside a Vaadin 10+ Flow application.
Issues can be reported on the MPR issues public repository.
Step by step migration guide
Follow the Migration Guide to configure your project to use MPR and port your legacy application to Flow
Configuration and advanced topics
Using Legacy Components In a Flow Application