Are you looking for a Desktop or Laptop?
What is your budget?
If a desktop system is required, then you can use an AMD CPU with a compatible dGPU. Here is a link to the current support for AMD dGPU's -
https://dortania.github.io/GPU-Buyers-Guide/modern-gpus/amd-gpu.html#native-amd-gpus. Do not make the mistake of thinking a dGPU supported in a desktop will automatically work in a Laptop when running macOS. You will also find the most current dGPU's are really expensive due to the Bitcoin mining expansion. A decent graphics card that previously would have cost £300-£400 now costs £1,600+, which is just mental.
If you want to dual boot and game only in Windows then an Intel i5 or i7 Laptop would be fine. Most laptops use 'Switchable Graphics' which in Windows is fine but not for macOS. You would need to disable the discrete GPU and just use the Intel iGPU for graphics in macOS. This is normal for most Laptop hacks.
High-End laptops come with good discrete GPU's but are expensive and usually quite large, i.e. desktop replacement systems, or more commonly mobile Workstations. The ones I have seen recently tend to come with just the IGPU or Nvidia graphics. You would need to make sure the mobile workstation doesn't come with 'Switchable Graphics' as they aren't supported in macOS.
Last but not least you could look at a buying an Intel MacBook Pro, possibly second hand/refurbished.