The Universal Character Sheets have tabs for organizing the type of information the character might need.
When a tab is created, the default is that the contents of the tab is viewable by everyone, but only editable by the owner.
The three dot menu in the tab label allows for a tab to be made hidden. The tab's contents and it's existence is then only viewable by the owner and the GM (if separate people).
Here is an example of the three states for tabs:
The tab is viewable by all - no icon.
The tab is hidden and being viewed - yellow eye icon with a diagonal strike.
The tab is hidden and not being view - grey eye icon with a diagonal strike.
A hidden tab can be a great way to hide your backstory, loot, conditions and abilities from your fellow players.
It can also be a place for GM and Player to communicate secretly via text (which can be done by both at the same time in the same hidden tab), as well as a great place to drop handout images that are meant only for that player's eyes.