How to group multiple different tables for a Many to Many Relation

Hey all, I'm working on a project an I needed some help in the database design.
The project is a platform in which the user can upload a video, write a blog, or create a course.
Each of them has its own table without any connections, but now I need the user to be able to bookmark the content.

The question is, should I make a separate bookmark table for each content type? I was also thinking to make a table called content, that contains only an id field, then each of the content types will add a contentId field as a foreign key (or maybe also a pk), now I can make a bookmarks table containing a userId and a contentId, but I think I'll have a hard time querying the bookmarks and trying to find the data of the content.

I'll really appreciate your opinion on this, thank you all.

Comments

[Pacharapol Withayasakpunt]

For SQLite, I would json_group_array or group_concat.