Thank you everyone for the replies!
So I guess that upgrading my CPU might be a better choice because it bottlenecks my system.
Thank you for telling me that the i9 9900k is not worth it just for gaming, but I'm still wondering which CPU I should get.
I was choosing the i9 9900k because I didn't wanted to upgrade for a long time but if there's a CPU that would last me a while and outperform the next-gen consoles (PS5/ Xbox Series X) please let me know, how good is the r5 3600? I always used Intel and NVIDIA so I don't know much about AMD's performance.
And I'm also thinking that my GPU (RTX 2060 non super) will be weak and mostly VRAM limited (6GB) in future games.
I also know that the advantage that the consoles have is that the games are coded to the metal, in other words they are mostly very optimized for the respective console.
For example, I was playing Need for Speed Heat on PC and even at the lowest settings I couldn't achieve a consistent 60fps, so I used the NVIDIA Control Panel and chose "Adaptive Half Refresh Rate V-Sync" and I got a consistent 30fps but after playing it on PC at those frames and play testing it on a PS4 Pro, I noticed that the PC had way more input lag compared to the console, so that's another point that I'm confused about...