Let's consider ten thousand forks.

  $ cat winforktest.sh
  #!/home/busybox-1.35 sh

  i=1; while [ $i -lt 10000 ]; do (echo $i); i=$((i+1)); done

On Linux, this takes:

  $  cat /etc/redhat-release
  Red Hat Enterprise Linux release 8.10 (Ootpa)

  $ time ./winforktest.sh > /dev/null
  real    0m0.792s
  user    0m0.490s
  sys     0m0.361s

On Windows,

  c:\users\x>ver

  Microsoft Windows [Version 10.0.22631.5472]

  c:\users\x>busybox | busybox head -2
  BusyBox v1.37.0-FRP-5236-g7dff7f376 (2023-12-06 10:31:32 GMT)
  (mingw64-gcc 13.2.1-5.fc39; mingw64-crt 11.0.0-2.fc39; glob)

  c:\users\x>busybox sh

  ~ $ time ./winforktest > /dev/null
  real    3m 44.44s
  user    0m 0.32s
  sys     0m 4.90s

Windows is quite a bit slower, at least with Busybox.

I understand that WSLv1 presents a more efficient fork(), which is not really available to shims like Cygwin or mingw.