I have an M.2 with linux (Pop OS) installed and windows on a HDD and Samsung SSD. Where do I install GRUB? My main OS is linux but i have certain programs that function best in windows. Wondering where to install the GRUB loader for a smooth experience, thanks.
None of those operating systems use GRUB.
Pop OS uses systemd-bootd, and Windows uses whatever it uses.
If your using UEFI booting its usually the best to have each drive with its own separate EFI partition, in this case the M.2 with Pop Os using systemD-bootd and the Samsung SSD with the Windows bootloader. if you installed in this way you should see boot options for both “Linux Boot Manger” and “Windows Boot Manager” in your UEFI boot options and just select which one you want to use.