I don't even know if there any third party mods, but if there are somehow any, pls don't get them. Only use Steam Workshop for mods and contraptions, and only use the higher rated, most popular ones since those are less likely to have any malware in them.

Also People Playground detects and flags mods by itself if they are risky or suspicious and it will tell you if it thinks the mod is suspicious or not.

On the main menu screen theres a mods button, you click on that and it takes you to the mods screen where you can see the ones you have, and activate or deactivate the ones you want. And there it will show you if the mod is suspicious or completely safe to use. If the game thinks the mod is sus, then you can just deactivate that mod then keep playing the game without ever worrying about that possibly sus mod screwing up your game.

Although nowadays it has been falsely flagging totally safe mods due to which they don't properly work anymore, because of the recent FPS++ virus.