Convert resolution 4096x2304 to 3840x2160 keeping the quality the same
Judge based on the quality rather than the bitrate value. Use CRF mode encoding and if the quality isn't what you can accept, decrease the CRF value.

ffmpeg -i "%%a" -s 3840x2610 -c:v libx264 -crf 18 -acodec copy D:\%%~na.mp4