Current GPUs come with hardware encoders built in. Nvidia GTX and RTX GPUs come with nvenc, Intel iGPUs come with Quicksync, AMD cards come with VCE. If you set the x264 "medium" preset as 100% quality, the quality of nvenc on RTX and GTX 16xx is also 100% quality, Quicksync perhaps 80%, VCE perhaps 60%.
Other external hardware encoders are not supported by OBS.
If you want to relieve your CPU from encoding and get the best quality, get some Nvdia RTX GPU, or GTX 1660/1660 SUPER or GTX 1650 SUPER for your PC.