I want start Gog Galaxy manually but It starts automatically when Windows start. Can I stop this? How?

I think somewhere in the settings of GOG Galaxy there is an option to set it off.

Otherwise you have to go to the Windows manager thingy where you can manage what programs start automaticly
https://www.howtogeek.com/74523/how-to-disable-startup-programs-in-windows/

Do you have Windows 10? There was an update recently. Windows 10 now "remembers" which programs you left running when you shut down your PC. If you don't turn off Galaxy before shutting down your PC, Windows will start it again when you turn on your PC.

Windows doesn't do this with all programs, but it does it with Galaxy. So, if you don't want that Galaxy starts when you boot your PC, you have to close Galaxy before you shut down your PC.

A few simple steps needed:

1. Uninstall Galaxy.

2. Uninstall Windows 10.

3. Uninstall the universe.

There, done. No problems whatsoever for anything or anyone, anywhere anytime.

Go to the GOG COM logo -> settings and you will find an option for it there. Uncheck start Galaxy at startup. Due note there was a recent issue with this due to how MS changed things in the Windows 10 Fall Creators Update but this should be fixed now as of the latest Galaxy update which is v1.2.31.

This worked! Thank you.