To chroot from the live USB into your installed system, you can try with the relevant tool in the Garuda Welcome of the live USB.
If not working, there is also a manual procedure here.
You should mount the "broken" btrfs system partition not the UEFI system partition.
sudo mkdir -p /mnt/broken
sudo mount /dev/nvme0n1p6 /mnt/broken
sudo garuda-chroot /mnt/broken/@
Change nvme0n1p6 with your system partition, if I did not pick up the right one.
When inside the chroot your have to mount the esp, which could be:
mount /dev/nvme0n1p1 /boot/efi
And proceed with the tutorial.
In general, do not use /dev/sda or /dev/sdax in the manual procedure. These are your USB key and relevant partitions.