Hello and welcome to Apple Support Communities, zeid225!
I understand you're seeing the bookmarks and Reading List bar every time you move your mouse too far over to the left. I'd be happy to provide information on how you may prevent this.
There is no way to disable this bar from coming up while you're on fullscreen, however, if you simply maximize the window, you can avoid this happening.
Manage windows on Mac
"Maximize or minimize windows
On your Mac, do any of the following in a window:
- Maximize a window: Press and hold the Option key while you click the green maximize button
in the top-left corner of an app window. To return to the previous window size, Option-click the button again. - You can also double-click an app’s title bar to maximize the window (as long as the option to do so is set to “zoom” in Dock preferences).
- Minimize a window: Click the yellow minimize button
in the top-left corner of the window, or press Command-M. - You can set an option in Dock preferences to have a window minimize when you double-click its title bar.
Most windows can be manually resized. Drag the window’s edge (top, bottom, or sides) or double-click an edge to expand that side of the window."
I hope this helps.
Have a great day!