Aside from being based on Fedora 39 now, KDE is now the official desktop environment replacing GNOME. The reasons why are in the article.
The GNOME version of Nobara still exists, but it's going to be the vanilla version shipped without any extensions (probably because many of them broke after moving to Fedora 39)
Why chromium is explained in the article (better support for many apps) but you can always change it to firefox, also detailed in the upgrade article.
I upgraded from 38 to 39 with no issues. It's honestly not hard or dangerous, just copy paste a few lines then paste the last ones to prompt the upgrade. The only catch is that if you had KDE already you won't need to remove some of the packages it tells you about. Don't overthink it imo.
Error:
Problem: The operation would result in removing the following protected packages: plasma-desktop
(try to add '--skip-broken' to skip uninstallable packages)