can't boot up to the linux kernel

[howtofixthis]

when the installation is allegedly completed, I get this screen, apparently my PC can't locate the linux kernel. I know that the problem must occur somewhere in the BTRFS mounting/formating/subvolumes but I couldn't find the error message from the outputs, I tried every command line by line so the procedure or the order of installing it must be somehow unfinished or wrong because I can't boot up to the OS.