1. Download/Create a dedicated server setup
2. Subscribe/Download one of the non recognized mods for example https://steamcommunity.com/sharedfiles/filedetails/?id=2614017981 then add it to server starting param (-mod)
3. Start the server
4. Open ArmA 3 Launcher and in mods / server browser try to find it, then click Join and in the dialog you can notice the mod is not recognized because its marked as red and does not allow to download it automatically