You’ve messed up partitioning and EFI partitions. There are leftovers from Debian and Windows. Wipe both drives, star fresh. Make one EFI partition on the NVME drive, 512MB, and use the rest for the main OS. Use the entire SATA drive for the other boot option (no need for EFI partition on that one). When installing the second OS, skip the bootloader install. Boot into the main OS, set grub to search for other OSes installed on the laptop and update grub afterwards. The second OS should appear in grub’s menu.