Show the {what} near the cursor, handle selecting one of the items with cursorkeys, and close it an item is selected with Space or Enter. {what} should have multiple lines to make this useful. This works like:

call popup_create({what}, #{
        \ pos: 'center',
        \ zindex: 200,
        \ drag: 1,
        \ wrap: 0,
        \ border: [],
        \ cursorline: 1,
        \ padding: [0,1,0,1],
        \ filter: 'popup_filter_menu',
        \ mapping: 0,
        \ })

The current line is highlighted with a match using "PopupSelected", or "PmenuSel" if that is not defined.

Use {options} to change the properties. Should at least set "callback" to a function that handles the selected item. Example:

func ColorSelected(id, result)
   " use a:result
endfunc
call popup_menu(['red', 'green', 'blue'], #{
        \ callback: 'ColorSelected',
        \ })

Can also be used as a method:

GetChoices()->popup_menu({})