Yes the post.hbs file is no more.
With it’s removal, 5 plugin-outlets are gone with it.
discourse/templates/post.hbs (5)
{{plugin-outlet “poster-avatar-bottom”}}
{{plugin-outlet “poster-name-right”}}
{{plugin-outlet “post-after-cooked”}}
{{plugin-outlet “topic-after-cooked”}}
{{plugin-outlet “post-bottom”}}
AFAIK (I haven’t tried yet) custom_fields and Widgets need to be used now