Mint :give root password for maintenance

And yes: for a few days i have problems with one of systems on my PC -LMDE. Recently i got repaired there one thing as shown here : (https://unix.stackexchange.com/questions/646652/mint-a-bunch-of-errors-in-boot) . Now i have yet bigger problem - system ask me password for non-existing user (root) error code is here: Give root password for maintenance (or press Control-D to continue): When i press these button it shows me: Reloading system manager configuration Starting default target You are in emergency mode. After logging in, type “journal -xb” to view system logs, “systemctl reboot” to reboot, “systemctl default” or “exit” to boot into default mode. Give root password for maintenance (or press Control-D to continue) When i chrooted into this OS (with live-boot) i saw that there are problems with sudo and pkexec, so i cant use root even in chroot (and modify system files, etc...) is there any way to boot PC normally or i need to always use “initramfs error” and boot only to busybox cli (i can do that because i accidentally uninstalled grub and now i have cli when booting up pc)? Ps: I didnt setted up root (su) account (no password, user, etc) and i was really messing up with sudo so now i think that this also doesnt exist. ———————————————- Edit: i’ve done it with passwd as @cas said. Now i have bigger problem. My second problem is that all my partition is r/o. Even with modified /etc/fstab to open all partitions as writable. My system didn’t exited cli to the now - system doesn’t load without writable permission and my current (logged-in) user looks like root (have # before command and whoami shows me as root) but it isn’t. When i try mount command they said that i need to have root permission ( how i cant have them when currently i am root?!). Is there something i forgot, all my PC is corrupt or im a real n00b?