During installation of Lubuntu 19.04, there is an option to Log in automatically without asking for the password.
Unfortunately, I can't find this setting anymore after installation.
I searched on the net but couldn't find any similar issues.
E.g. https://www.smarthomebeginner.com/enable-lubuntu-auto-login/
is for 12.04 or lower and there is no directory named /etc/lxdm/ or /etc/lightdm/ in 19.04.
https://www.maketecheasier.com/enable-automatic-login-in-ubuntu/
is for Ubuntu and there is no Automatic Login setting in User Accounts.
There is a section in the Lubuntu manual that deals with this :-
https://manual.lubuntu.me/stable/3/3.1/3.1.9/sddm_configuration.html
To enable auto-login, you do the reverse (ie. add the line) but I would suggest reading it in the manual (it's better formatted than I can do)