How to limit number of cores PyCharm is using?

I was trying to follow PyCharm docs here https://www.jetbrains.com/help/objc/how-to-adjust-cpu-cores-number.html 

and tried finding cidr.indexer.thread.count, but it does not exist in my Registry. Why so?

How do I leave 1 CPU available for basic tasks? I cannot use my entire PC because one process parallel and PyCharm gives 100% of CPU capacity to this one process.