I am the most recent admin of fan-posts.fandom.com and I saw that it's main page isn't up to date, so I edited it. (not vandalism, just made it up-to-date) anyways, editing main pages is against fandom rules? I am a newbie here.
I am not sure why you would think that. There is no global rule preventing users (even non-admins) from editing the main page of wikis. However, most wikis do restrict editing of the main page to admins/content mods. As a matter of fact, editing the main page to improve the layout and update information is strongly encouraged.