You can define a variable then put everything in the side menu screen under an if statement. So
default side_menu_vis = True
screen side_menu():
if side_menu_vis:
add "gui/qm/side_bg.png" xalign 1.0 at side_float
add "gui/qm/menu_bg.png" xalign 1.0 offset (-50, 50) at side_float
vbox:
at side_float
style_prefix "side"
textbutton "Quick Save" action QuickSave()
textbutton "Quick Load" action QuickLoad()
textbutton "Save" action ShowMenu("save")
textbutton "Options" action ShowMenu("preferences")
textbutton "History" action ShowMenu("history")
textbutton "Main Menu" action MainMenu(confirm=True)
Then you can control the accessibility of the side menu by turning the variable (side_menu_vis in this case) True or False.
The regular quick menu (back,auto,skip) already has a variable for this, it's quick_menu