Parkfans.net has a main focus on Busch Gardens Williamsburg and Kings Dominion, but they do cover all parks on their forums and are well moderated.
https://parkfans.net/
The rollercoasters subreddit on reddit is great for keeping up with the latest information and trip reports.
https://old.reddit.com/r/rollercoasters/
The Inside Universal forums mainly focuses on Universal, Seaworld, and Disney parks. They have some discussion on other parks, but that is a bit limited. The Six Flags Magic Mountain topic is pretty active.
https://forums.insideuniversal.net/
The Coliwood Studios youtube channel posts often about Great Adventure news.
https://www.youtube.com/@ColiwoodStudios/videos