The plugin repository is the one in nodebb admin. But the thing about it is that there is no moderation there - it's just npm packages that have nbbpm attribute and compatibility string. If the compatibility string is wrong, there is no way for NodeBB to verify that. You can learn about it here.
Other than that you can just search GitHub, NPM and GitLab for names starting with nodebb-plugin.
Plugin to automatically create topics & opening post from Twitter, Youtube acc's etc. etc.
Is there a plugin that automates the following - for example, watching a twitter account or youtube account and grabbing the title and link to the latest posts to an acc or channel to create new topic for each new event at the watch targets.
populate opening post: Title + link etc. etc.