Is it possible to "undo" a raid1 configuration

Easiest way is to reinstall the system without RAID 1.

If that is not possible, then you need to first take backup of current system and then start into a recovery system to move partitions around.

These are high level instructions of the steps to take. Notice that /usr and /var directories are moved from their own partitions to / partition. This can cause problems in the future, if /var directory grows to fill the root partition.

After booting up the recovery system:

1. Mount /dev/md2 to /mnt
2. Create /mnt2 directory.
3. Mount /dev/vg0-usr to /mnt2.
4. Move all files from /mnt2 to /mnt/usr.
5. Unmount /dev/vg0-usr.
6. Mount /dev/vg0-var to /mnt2.
7. Move all files from /mnt2 to /mnt/var.
8. Unmount /dev/vg0-var.
9. Mount /dev/vg0-home to /mnt2.
10. Move all files from /mnt2 to /mnt/home.
11. Unmount /dev/vg0-home.

Now, the /dev/md4 device and volume groups under it can be removed.

1. Run vgchange -a n vg0 to deactivate vg0 volume group.
2. Run vgremove vg0 to remove the group.
3. Run mdadm --stop /dev/md4 to stop RAID device
4. Run mdadm --remove /dev/md4 to remove the RAID device.

Create a RAID0 array for new volume group and create logical volume for /home:

1. Run mdadm --create /dev/md4 /dev/nvme0n1p2 /dev/nvme1n1p4 --level=0 --raid-devices=2
2. Run pvcreate /dev/md4.
3. Run vgcreate vg0 /dev/md4.
4. Run lvcreate -l 100%VG -n home vg0
5. Run mkfs.ext4 /dev/vg0-home
6. Run mount /dev/vg0-home /mnt2 to mount new home directory.
7. Move files from /mnt/home to /mnt2.

Last step is to modify fstab so that system doesn't try to mount non-existing logical volumes during startup. Edit /mnt/fstab and remove lines that contain /dev/vg0-var or /dev/vg0-usr.

After these steps, you can reboot the machine and your /home should be what you wanted.