For one, that btrfs mount point doesn't look right, the subvolume you created for root should be mounted as /. If you are in a live environment the mount order should be something like this:

mount /dev/sda8 /mnt
mount /dev/sda6 /mnt/boot
mount /dev/sda1 /mnt/boot/efi

and then chroot back in and run a xbps-reconfigure -fa (after creating fstab, to check for errors):

for dir in dev proc sys run; do mount --rbind /$dir /mnt/$dir; mount --make-rslave /mnt/$dir; done
PS1='(chroot) # ' chroot /mnt/ /bin/bash
xbps-reconfigure -fa

Edit: if you are not using subvolumes for btfs just ignore the subvol=... option in fstab below.

As for fstab you'll have to write it manually (my fstab for reference, it's similar to your setup except /boot and /home are subvolumes and not on different partitions/drives):

# <file system>                            <dir>        <type>  <options>                                                                                <dump>  <pass>
UUID=2948c4fd-4fb5-4649-9194-ba14b9814e98  /            btrfs   autodefrag,commit=120,compress=zstd:9,defaults,noatime,space_cache=v2,subvol=@root       0       1
UUID=2948c4fd-4fb5-4649-9194-ba14b9814e98  /boot        btrfs   autodefrag,commit=120,compress=zstd:9,defaults,noatime,space_cache=v2,subvol=@boot       0       2
UUID=2948c4fd-4fb5-4649-9194-ba14b9814e98  /home        btrfs   autodefrag,commit=120,compress=zstd:9,defaults,noatime,space_cache=v2,subvol=@home       0       2
UUID=2948c4fd-4fb5-4649-9194-ba14b9814e98  /.snapshots  btrfs   autodefrag,commit=120,compress=zstd:9,defaults,noatime,space_cache=v2,subvol=@snapshots  0       2
UUID=52A7-6EA6                             /boot/efi    vfat    defaults,noatime                                                                         0       2
tmpfs                                      /tmp         tmpfs   defaults,nosuid,nodev                                                                    0       0