Adding Multiple Configurations While Dual-booting

Beginner here. I was trying to add a configuration to the Grub 2 bootloader, but running

sudo nixos-rebuild boot

is just not going forward.

Currently on NixOS Ver 24.05 dual booted on the same disk with Linux Mint (where Mint was downloaded first). There are four total partitions, with Mint on sda3 and Nix on sda4.

The following are the logs after running the command. Help is always appreciated.

building Nix...
building the system configuration...
updating GRUB 2 menu...
Warning: os-prober will be executed to detect other bootable partitions.
Its output will be used to detect bootable binaries on them and create new boot entries.
lsblk: /dev/mapper/no*[0-9]: not a block device
lsblk: /dev/mapper/raid*[0-9]: not a block device
lsblk: /dev/mapper/disks*[0-9]: not a block device
Found Linux Mint 21.2 Victoria (21.2) on /dev/sda3

Perhaps you have two GRUBs and you were booting the Mint one?

When linux mint was installed, it wouldn’t launch through the grub bootloader, just the regular bios screen then launch. After installing NixOS, the grub launcher opens every time I start my machine.

If that were the case, how could I know?

Does you GRUB say “NixOS”?

No. It’s titled GNU GRUB Ver 2.06.

On it I have five options to boot, Mint, Advanced Options for Mint, NixOS, Advanced Options for NixOS, and UEFI. If I select Advanced options for Nix, I find two configurations, the base, and one called Configuration 1 which was made months ago.