The main menu for Casual I-Search is organized into the following sections:
Commands to edit the search string. The type/extent of the string (word, symbol, line, thing) can be specified here.
Invoke query-replace or query-replace-regexp on matched strings.
Commands to configure the type of search. Toggling any menu item in this section will dismiss the Transient menu and return you back to the I-Search minibuffer prompt.
Miscellaneous commands. From here the search string can be fed into occur or be highlighted.
Navigation commands for matched strings.
When in search mode (typically via the keybinding C-s or C-r), pressing the keybinding C-o (or binding of your preference) will raise the Transient menu casual-isearch-tmenu. Once raised, only the I-Search commands in the Toggle, Replace, and Misc sections will automatically dismiss the menu when selected. All other I-Search commands will not dismiss the menu.
Use C-g to dismiss this Transient menu.