I got two warnings for the mkinitpcio
==> WARNING: Possibly missing firmware for module: 'xhci_pci'
==> WARNING: consolefont: no font found in configuration
and further for sudo update-grub
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.
Adding boot menu entry for UEFI Firmware Settings ...
Root filesystem isn't btrfs
If you think an error has occurred, please file a bug report at "https://github.com/Antynea/grub-btrfs"
Found memtest86+ image: /boot/memtest86+/memtest.bin
/usr/bin/grub-probe: warning: unknown device type nvme0n1.
done
Don’t know if this helps.