Database design for social media app: Handling multiple post types and timeline creation performance

Question

We're designing a relational database for a social media-like application. In this application, we have 7 different types of posts, each with 2-3 unique fields. To simplify development, we're considering storing all these fields in a single entity called PostContent instead of querying and sorting them separately based on the post type when creating a timeline.

However, this approach leads to a significant number of null values in our database.

Additionally, in our system, we'll create a new timeline for the communities it's associated with and their users every time when a post is created.

Since the timeline creation service will be heavily used in our app, would our current approach cause serious performance issues? What would be the best way forward in this situation?