[Baertram]

I do not know any button addon and non to quit the dungeon but the addon "Simple Group Leave" got some slash commands for the chat e.g.
/gl
/groupl
/groupleave
/leavegroup

https://www.esoui.com/downloads/info...shcommand.html

You could download this one and add the function call named above by Dan to the code in the file SimpleGroupLeave.lua,
inside function SimpleGroupLeaveAbandon:

SIMPLEGROUPLEAVE = {}
SIMPLEGROUPLEAVE.version = 0.6
SIMPLEGROUPLEAVE.author = 'DeanGrey, modified by Baertram'
 
function SimpleGroupLeaveAbandon()
    if not IsUnitGrouped("player") then return end
    GroupLeave() --leave the group
    ExitInstanceImmediately() --Exit the instance
end
local leaveGroup = SimpleGroupLeaveAbandon
 
SLASH_COMMANDS["/gl"]           = leaveGroup
SLASH_COMMANDS["/groupl"]       = leaveGroup
SLASH_COMMANDS["/groupleave"]   = leaveGroup
SLASH_COMMANDS["/leavegroup"]   = leaveGroup