Hello there @OfficialPloxed!
Checking through your log, and considering that standalone works fine, the most likely cultrip is a conflict with steam_api64.dll, following the lines below:
[Callstack] 0x00007ff60f59b71b Mischief_Madness.exe!_tailMerge_steam_api64_dll()
[Callstack] 0x00007ff60c6635bc Mischief_Madness.exe!USteamProFriends::USteamProFriends() [F:-=Unreal=-\Mischief_Madness\Mischief_Madness 5.5\Plugins\SteamCor77fed6fa6641V9\Source\SteamCorePro\Private\SteamFriends\SteamFriends.cpp:49]
Standalone does not need steam_api64.dll to start, but the packaged build will check for that .dll, so the first step is to check if the file is present, please check your Binaries folder. If this is the case, then test doing a clean rebuild, via deleting Binadies and Intermediate folder, then re-generating project files, and try to pack again.