Spring Webflux apps non-blocking, but starts using "main" thread

Question

Small question regarding Spring Webflux web apps please.

Webflux apps are well known they should not block. However, on each of my application startup, I do see:

logger_name:  org.springframework.boot.web.embedded.netty.NettyWebServer 
    message:  Netty started on port 8080 
    thread_name:  main 

logger_name:  a.b.c.MyApplication 
    message:  Started MyApplication in 251.887 seconds (JVM running for 52.801) 
    thread_name:  main 

And only after that, I see it is serving requests on thread such as [or-http-epoll-1], [or-http-epoll-2], [or-http-epoll-3], [or-http-epoll-4]

As you can see, the startup time is quite high. This is a bit confusing, as it uses the "main" thread, which I think is blocking, in order to perform application startup.

There are no code on my end using the main thread on purpose.

Hence, I am having a hard time understanding, why this use of main thread, if there is a way to use the non blocking threads instead?

Thank you