Application Command Manager (#5992)

Co-authored-by: Danny <1695103+Rapptz@users.noreply.github.com>

redbot/cogs/downloader/downloader.py

@@ -1625,6 +1625,12 @@ class Downloader(commands.Cog):
                             command=inline(f"{ctx.clean_prefix}cog info <repo> <cog>")
                         )
                     )
+            # If the bot has any slash commands enabled, warn them to sync
+            enabled_slash = await self.bot.list_enabled_app_commands()
+            if any(enabled_slash.values()):
+                message += _(
+                    "\nYou may need to resync your slash commands with `{prefix}slash sync`."
+                ).format(prefix=ctx.prefix)
         if failed_cogs:
             cognames = [cog.name for cog in failed_cogs]
             message += (