Install Windows first. The setup creates an EFI partition, most likely as /dev/sd?2. We’re gonna need that later. Then turn off fast boot. Enter
powercfg -h off
on the command prompt. Make sure that you have local admin rights. Fast boot is incompatible with dual boot. You’ll get blue screens with repair options otherwise. While at it, set the system clock to UTC. Create this DWORD registry key:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation\RealTimeIsUniversal
and set it to “1”.
Then install linux and mount /dev/sd?2 from above to boot. Then create a new file named arch.conf in /boot/loader/entries:
title Arch Linux linux /vmlinuz-linux initrd /initramfs-linux.img options root=UUID=$(blkid /root/partition) rw audit=0
The paths are relative to /boot, so vmlinuz-linux should be /boot/vmlinuz-linux. Next edit /boot/loader/loader.conf:
console-mode auto default arch timeout 5
Assuming that you’re using systemd-boot, run bootctl install and bootctl update, reboot and be happy!