Anyone know why I get low fps

So I built this pc around 2021 when prices were outrageous , but the problem I’m having is low fps on almost every game like counter strike 2 and Fortnite I get around 140 ish then they randomly drop like crazy , if anyone can help me by telling me if I should upgrade motherboard or cpu or something lmao .

What a minimum fps that I should be getting on this build ….