Don’t press “E”
that is for editing the config once you successfully got to that point
you are not there yet - and “E” will NOT get you there
It’s different keys that interrupt the sequence.
Like:
F1 or ESC or …
I just don’t know off the top of my head what will surely show you the now hidden menu
… try different keys from the top row …
Instead of trying to figure it out
or
instead of trying to edit the grub configuration
which you can’t seem to make work
just boot a live system - like … literally any linux ISO you have
you never reported back the result of:
You can easily force check your filesystem (if it is not BTRFS) using literally any Linux live ISO.
… but I have suspicion that it is going to turn out to be BTRFS …