Hey
Does anyone knows if its even possible to install the pack on a mac?
The file is .exe, so do i need to place it somewhere in the game folder for it to run, or is it just impossible?

Theoretically it's possible, as Stronghold is running within a Wineskin wrapper.
In Finder, simply try to drag and drop the .exe, onto the game. That could start a proper installation of Excalibur inside the wrapper, but it could also break the game, so keep a backup.

Tried that and i got the installer and installed, everything seemed good. But i got nothing in game, thanks for the help tho.

All the installer is doing, is extracting some map files into the game's "Map" subfolder.
Right-click or Cmd-click the app and open it with "Show package contents".
Inside go to drive_c/Program Files/GOG.com/Stronghold/Maps/ and check if the following maps are there:
Camelot.map
Edinburgh.map
Harlech.map
Haut-Koenigsbourg.map
Koblenz Stolzanfels.map
Mordred's Fortress.map
Tintagel.map
Tower of London.map

If so, the add-on is properly installed. If not, check if the Excalibur installer put them in another, wrong subfolder and move them manually into Maps.