Settings passwords for kali default user and roo for live encrypted persistent

Hi, I'm just new to Kali and Linux world. And I am using Kali live 2020.3 encrypted persistent.

I'm looking for a solution to change the password permanently for awhile. But only I can found are about version 2020.1.

I've read there is no root user for kali 2020.3. But I can use "sudo su" command without a password. And default kali user password is set, I can't change it (change it in terminal but after reboot it resets). There is no file called ?/lib/live/config/0031-root-password?. There is "?/lib/live/config/0031-kali-password? instead.

Actually I am really confused.

If I left the password as it is (nothing maybe), is it a vulnerability for Kali system?
It is not for physical vulnerability because persistent partition is encrypted.
But for online, everyone probably knows my root password (which not exists) or kali password. Do I need to change it every boot?

Thank you!