Upgraded to 3.0.2 from 2.4.6 -> problems

I’ve ugraded and all SSL certificate are unknown plus all sites gave 503 error.
I’ve exporte previously all sites and install fresh 3.0.2 (is lot slower then 2.4.6) but when i import a 2.4.6 4.9.xWP version inside 3.0.2 won’t work at all.

Why IPv6 slider not work?
Why Faster Docker Volums not ask any admin permission like before?

There is a way to choose what WP version install in a new website?

Is possible to return back to 2.4.6?