Maybe after all you need change user password, because when you run any command with sudo, it asks user password, for example - sudo apt get update
Also, when you run command with sudo, it has “root envirement”, so why, of course, sudo whoami returns root
After all, in a simple Lubuntu installation you even shouldn’t “unlock” root user (with setting up password for root), except for special cases
Meanwhile, there are actually a bug with swithcing non-English layouts in some places (for example, log on screen) after installing from LiveCD since Lubuntu 19.10, please see Can’t change keyboard locale on logon screen with lxqt (Lubuntu 19.04, 19.10 and 20.04)