Looking for suggestions for a good framework/platform for creating a site to host a collaborative single page web application

I had this idea for a collaborative single page web application a while back. The core idea is pretty straightforward, and the innovative part will probably not require a large amount of development. However, I quickly came to the conclusion that to do it properly, I really need a decent set of social media site-like features to provide the right level of support for the users using the site.

1. User accounts with secure logins, permissions, etc. and all that implies.
2. Private/public communication through messages, forums/chats, announcements, news, etc.
3. The creation, management, and moderation of collaborative groups by any user who wants to create a group to work on a project together.
4. Modern reactive look and feel.
5. Admin interface to manage the aforementioned items.

I have no desire to reinvent the wheel, and clearly, there must be a number of open source solutions out there already that replicate this type of functionality, so what I am looking for the best CMS framework or platform that provides these features, and would allow me to focus on the my single-page application and interfacing it with rest of the features.

Anyone have any suggestions? The only CMS system I have any extensive experience with is WordPress and it doesn't really seem like a good fit in this case. Is BuddyPress worth a look instead?

I have experience with PHP, Javascript, SQL, and various frameworks (Laravel, Vue, etc), along with WordPress, if that's any guide.

Thanks for reading!