120hz vs 90hz

Hello everyone, I’ve been playing with settings for a year now and I get most of it but there is still something that boggles me. Whenever I set the refresh rate to 90 HZ or less I get the worst performance than if I set it at 120 HZ. How can this be? I read on forums that if your system cannot handle higher refresh rate you should lower it, but in my case it’s the opposite. Thank you for clarifying.
System: i7-9700f
3070
32Gb RAM

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