You cannot rename a file from webp to jpg, but you can change the URL to .jpg and it will likely serve you the jpeg version. You can also convert webp to another format with dwebp or MS Paint.

There are many ways to run code at startup. cronjobs and systemd are common ways to handle this. I have also had things start automatically with my desktop environment which comes later in the boot process.

You may be accustomed to the process, but fixing issues in the registry is not intuitive. It is simple enough if you find a guide that tells you exactly which item you need to work on and exactly what the default is and what you need to change it to, but what if the guide isn’t exactly what you want?

In the GNU/Linux ecosystem, nearly every program has a config file. Sometimes each line has detailed comments in plain text around it you what the option does with examples of what it could be. If the documentation doesn’t exist, you can dig deeper and see what that option does in the source which is usually documented as well. Programming experience is not required to search for text and read comments. Such documentation is not equivalent in Windows.

You were hacked by the manufacturer.