I have three ideas: First, you could switch the desktop environment to one of the ones that has a GUI settings tool to set passwordless automatic sign in. I think Gnome 3 on Ubuntu, and Mate Desktop on Linux Mint have that feature. There are probably others.

Second, you could switch your display manager to "nodm". The display manager is the thing that runs the X server or Wayland, and it starts the greeter (the greeter is the program that shows the login screen). nodm is a special display manager that doesn't use a greeter or ask for a password. It immediately starts the session using the username and desktop environment specified in its configuration file.

I use nodm for my HTPC and it works very well. The only downside is that you have to edit its configuration file, /etc/default/nodm , using a text editor. I'm not aware of any GUI configuration tool for it. However, it's pretty easy to configure.

Third, you could abandon all display managers, and start the session manually, either from a shell script, or over SSH. This is a little more complex. You will probably want to get comfortable with SSH before trying this (SSH is the command-line analog of remote desktop).