ZO_WorldMapInfoMenuBar is not just menu bar, but scene fragment bar (menu bar with added functionality).
To add button you need to use function:
Lua Code:
ZO_WorldMapInfoMenuBar:Add(name, fragmentGroup, buttonData, keybindButton)
So, if I update your code:
Lua Code:
local buttonData = {
normal = "EsoUI/Art/mainmenu/menubar_journal_up.dds",
pressed = "EsoUI/Art/mainmenu/menubar_journal_down.dds",
highlight = "EsoUI/Art/mainmenu/menubar_journal_over.dds",
callback = function(...) d("callbackdata") end,
}
local bossFragment = ZO_FadeSceneFragment:New(control) --control is your stuff you want to show/hide
ZO_WorldMapInfoMenuBar:Add("Boss Drops", {bossFragment}, buttonData)