MySQL Router 8.4 Release Notes
Important Change: MySQL Router no longer supports MySQL Server versions from a newer series. The metadata is checked and discarded for servers from a newer series, a check that executes during bootstrap and during periodic metadata refresh operations. A newer version in the same series is supported. For example, MySQL Router 8.4.4 supports MySQL Server 8.4.5 but not MySQL Server 9.0.0. (Bug #36041256)
        Because building with CMAKE_BUILD_TYPE=Debug
        disables optimizations, std::vector.resize()
        attempted to initialize every byte before each read from an
        encrypted socket. Memory usage was improved to account for this.
       (Bug #37385923)
        Accessing the /routes/{name}/connections REST
        API endpoint while also benchmarking queries through the router
        could cause the router to unexpectedly halt.
       (Bug #37251508)