Boost asio if you love C++ and asynchronous networking.
I switched out asio's epoll backend for its io_uring in a database server and CPU utilization shot up. Probably depends on usage and the specifics of how it's integrated into the event code.
Boost is so inconvenient, they're huge dynamic libraries that are a pain to build and use. Even when I was already using CMake, getting Boost installed in a way where it could be discovered was super annoying. (I was on Mac, though)
I’ve replaced Asio recently with stright epoll event loop and got about 16% RPS better. That is for resonably sized SQL server, so be careful with nice precanned libraries.