I'll try to test this patch, possibly today.

Is the patch from the 18th of March the right one?
The patch says it has 5 components but the last patch is

--8<---------------cut here---------------start------------->8---
[PATCH 4/5] bootloader: grub: Allow booting from a Btrfs subvolume.
--8<---------------cut here---------------end--------------->8---

Is the fifth patch missing?

-- 
Pierre Neidhardt
https://ambrevar.xyz/