View to display content type and media type Drupal 8
Say I have 1 content type and 2 media types users can create
Content type: Post
Media Type: Picture
Media type: Movie
How can I create a view that pulls all 3? As far as I can see you can only create views that show content, or media but not both in the same view.
I wasnt to create a feed displaying all 3 types of all users on the site.
If there are no relationships among the three entity types, as you have indicated in comments, you could use attachments or blocks. (I'm assuming you want a page that displays all the information.)
Attachment Solution:

Create your View with a page display of one of the entity types.
In the same View create two attachment displays, and use overrides to base them off the other entity types. Attach them to the page display.

Block Solution:

Create your View with a page display of one of the entity types.
Create additional, separate, Views of each of the other entity types, with block displays
Use the block configuration system to place those blocks on the page display