When I downloaded FileZilla, somehow I also got Chromium and some TV something downloaded and installed under Win10. I removed the TV crap, really no need, but I was thinking to keep Chromium since I need to test my websites with it once in a while. Cool, but that stupid software installed itself to auto-start!!!

I don't think I had the option to NOT have such a feature turned on.

So... I had to search for it because apparently no one knows how to handle Auto-Start features under newer versions of MS-Windows. It is actually... take a deep breath... in the Task Manager. (At least in Win10).

So, you right click on the taskbar, select Task Manager, and in there click on the tab Startup.

There is a list of the processes that will get started on each reboot. Right click on Chromium and select Disable. Now it won't auto-start anymore.

I have not seen an option to completely remove the entries. But as long as I don't get a full screen window after a few seconds of rebooting while trying to do something else, like starting FireFox, I'm happy.