UEFI PC #4:
ara88:~ # grep RETT /etc/os-release
PRETTY_NAME="openSUSE Tumbleweed"
ara88:~ # ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
ara88:~ # df /sys/firmware/efi/efivars/
df: no file systems processed
ara88:~ #
[root@ara88 ~]# grep RETT /etc/os-release
PRETTY_NAME="Fedora Linux 40 (Forty)"
[root@ara88 ~]# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
[root@ara88 ~]# df /sys/firmware/efi/efivars
df: no file systems processed
[root@ara88 ~]#
root@ara88:~# grep RETT /etc/os-release
PRETTY_NAME="Debian GNU/Linux trixie/sid"
root@ara88:~# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
root@ara88:~# df /sys/firmware/efi/efivars
df: no file systems processed
root@ara88:~#
[root@ara88 ~]# grep RETT /etc/os-release
PRETTY_NAME="Mageia 9"
[root@ara88 ~]# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
[root@ara88 ~]# df /sys/firmware/efi/efivars
df: no file systems processed
[root@ara88 ~]#
root@ara88:~# grep RETT /etc/os-release
PRETTY_NAME="Ubuntu 24.04 LTS"
root@ara88:~# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
root@ara88:~# df /sys/firmware/efi/efivars
df: no file systems processed
root@ara88:~#
root@ara88:/etc# neofetch | grep OS
OS: MX x86_64
root@ara88:/etc# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
root@ara88:/etc# df /sys/firmware/efi/efivars
df: no file systems processed
root@ara88:/etc#
root@ara88:~# grep RETT /etc/os-release
PRETTY_NAME="Ubuntu 24.04 LTS"
root@ara88:~# ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
root@ara88:~# df /sys/firmware/efi/efivars
df: no file systems processed
root@ara88:~#
ara88:~ # grep RETT /etc/os-release
PRETTY_NAME="openSUSE Leap 15.5"
ara88:~ # ls -1 /sys/firmware/efi/efivars/ | wc
77 77 3826
ara88:~ # df /sys/firmware/efi/efivars
df: no file systems processed
ara88:~ #
Like I wrote already, here and in the bug report, I cannot not reproduce here. Every PC, every OS, same result.