For 1440p / 4K you'll need a 6800XT or better from AMD or 3080 or better from nVidia.
Do you have a preference for any particular brands? AMD/Intel/nVidia? Do you have any particular size requirements for the case (need really small vs don't care if its really big) ?
Here's a starting point for debate, using an AMD CPU and an nVidia GPU:
I started with "only" a 3080 but there is also the 3080 Ti, 3090, and 3090 Ti above that. My preference is to get close to the top end without going all the way. For example I have a 5950X and an RX 6800XT and I expect to get at least 5 years out of this combination. So in my opinion, a 3080 will also last a good while. Your preference may vary. There's plenty of headroom left in your specified budget range to go all the way to a 3090.
PS - I didnt include any peripherals like keyboard or monitor since I dont know what you might recycle from your current system and those things are really subject to personal preference.
Just one helpful comment to make. If you want to future proof yourself, usually a bigger power supply will help. Intel 13th gen and Nvidias 4000 series are said to have a lot more consumption of power, 850W is starting to become the new standard in minimum spec. Make sure you get a comparable case with good airflow as well, will help your parts last longer.
You can always come into a Micro Center and speak with one of the Build your own specialists, they know what the best is for the best prices.
Personally, I do recommend Nvidia GPUs, they have a lot more support by triple A title developers, better software and drivers. Most of nvidias technologies are used by game developers like DLSS and RayTracing. DLSS is great if you want to push 4k.
Submit photos and a description of your PC to our build showcase
See other custom PC builds and get some ideas for what can be done
Services starting at $149.99