RetroPie is just a RaspiOS Lite image underneath, so a regular Linux/Debian installation.
You can add your code to the autostart.sh script that RetroPie uses to start EmulationStation (see here how to access the script) or just create your own service to start on boot (see here).

@megas "3B+" is the same as "3" in this instance. This will work for you.

Did you wait a while to let the disk check finish?

Is lowering the resolution an option to you? And using overlays and shader can also have an impact.