It depends. In US, flight schools operate under two FAA regulations: Part 61 and Part 141.
A Part 61 regulation does not have a specific time requirement for ground school, you can do self-study and take the written exam with an endorsement from an instructor. Part 141 operating flight schools are more pilot career oriented and have specific time requirements.
For getting a PPL under part 61, you can do some online ground school like King Schools (mentioned above), Sporty’s, MzeroA, Rod Machado’s courses - there are several options. After completing the ground school you will be given an endorsement with which you can take the FAA written exam.
If you just want to learn for simming purposes and don’t wish to spend money in the beginning, you can even check out a couple of free online ground schools. They provide quite an overview of the topics that you need to learn and can give you a great insight before going for in-person training.
I suggest these ones (you can learn at your own pace):
MIT Opencourseware: https://youtube.com/playlist?list=PLUl4u3cNGP63cUdAG3v311Vl72ozOiK25
Fly8ma Free ground school: 2021 FREE Private Pilot Ground School Pilot Course | FLY8MA