Huh, that's annoying.
Thanks for pointing me in the right direction though. Apparently using alt-F4 on the desktop to shutdown stops this behaviour too.

Supposedly if you log in with a Microsoft account there's something in the Cortana settings that can disable it, but if you don't use an MS account you can't even get at those settings, and apparently it doesn't always work anyway.

There's probably a registry hack somewhere for it, but I'd be leery of that mucking things up in a future update. (But if you do use an MS account, might as well poke around the Cortana options, too.)

Ah ok. So it seems this is Microsoft's "answer" to the cases where Windows 10 suddenly just decides to reboot the machine while one is still working on it (W10 has applied an OS update in the background, and forces a reboot).

This happened to me once as well, I was browsing the web when W10 suddenly just decided to reboot, apparently due to updates. If there was any warning, I didn't see it, maybe it was in the background.

Yup. Because there's never a time when I may be doing something important that a shut down will be catastrophic to either the work or to the computer. I love how Microsoft is taking control away from its end users in the name of convenience.

Win10 does not reopen all programs that are left open when you shut down. Just tried it with the following programs running:

Thunderbird (email)
Firefox
Excel

Only Excel opened automatically when I did a hard shutdown and reboot; same result with a warm reboot. I have not made any startup changes since installing the Fall Creator's Update a week or so back.

It *may* be possible for gOg to change this restart behavior on their end, though they may not *want* to change it.

A program must be compiled with a special flag to exhibit this behavior (don't recall what said flag was, allow_hibernate or something). GOG has already said that this behavior will be fixed in the next Galaxy update, so I guess they'll remove said flag.

Thanks, JMich. Not a Galaxy user so I don't keep up with those details but I've read a few threads recently talking about this behavior, and thought to myself, "Um, it hasn't been doing that on my machine..." So I tested it. : )

Did you try shouting at it?

well apparently you cant just disable it in the client (thats what i came here for to find out).

so i just disabled it in windows autostart.
problem solved ;)

win7
search: msconfig - select the tab for startup remove the ckecked box from GOG.
save and restart.
GGWP

You can actually. Click the GOG logo on the top left, settings, then find the "Start Galaxy when Windows Start" checkbox and remove it.

Sorry this is coming so late, your question being a year and a half since past, but I found a setting in GOG (a recent version from Oct. 2018) when the main window is open. Click on the upper right GOG logo to drop down the menu, and select "Settings". The general settings tab has a check box option to control startup of GOG when Windows starts.

For posterity,
Burndoubt