You should ask all users to create private topics to get such a result. You can use the wpForo Admin note/message feature. More info here: https://wpforo.com/community/postid/20205/

Here is a similar case and solution to force creating a private topic: https://wpforo.com/community/how-to-and-troubleshooting-2/set-all-topics-to-private-by-default/

Also, as it's announced on the top of this forum, this support forum is only related to the addons. If a question or an issue is related to any feature of the core wpForo plugin, you should open it in the wpForo plugin support forum.

Any post/theme, which will be create any user, will be hide from another users.

As example: user "A" was create a post, and user "B" was create a post, and this users can't see posts anothers, user "B" can't see posts "A" and "A" can't see post's "B".

But without button - private theme (because some users can forgot click to this button, and post will see all users) How by default make this, without told any users to click button "private" when they a creating post... 

And how to boost Max File size? as from 10mb to 30mb...