Hi,
Just want to make sure this issue with Samsung Chromebooks is on your radar, see https://archlinuxarm.org/forum/viewtopic.php?f=47&t=15169 for discussion. The long and the short of it is that the system doesn't seem to recognize that the boot flash is bootable when a 5.11 kernel is flashed to it. Downgrading to a 5.10 kernel fixes things.
-m3lang3
EDIT: This problem appears to affect both Samsung Chromebooks 1 (XE303C12) and 2 (XE503C32); also modified the subject to make this clear.