Can I use C# Multithreading To Instantiate GameObjects?

If I use Unity’s Job system then I cannot instantiate GameObjects using jobs.
Could I instantiate GameObjects on a seperate thread using C# multithreading(System.Threading)?

No, you can not. Unity’s scripting layer is for the most part single threaded and most of the API functions are not thread-safe. Though it’s not only about thread safety but Unity actually prevents most of these method to be called from any other thread by throwing an exception if you try.

You can prepare pure data on your own background threads but the actual GameObject and component creation has to be done on the main thread.

What @Bunny83 said.

Also, if instantiation gives you performance problems, consider using pooling with pool warmup on start.

This will allow you to choose when Instantiate() call happens (game start, for example) and replace existing calls with an equivalent of SetActive(true).