Today I installed No Man's Sky again. Everything worked fine I thought but now it's not possible to start the GOG Galaxy client. I got the message about missing libraries such as

MSVCP140.dll
VCRUNTIME140.dll

Uninstalled and reinstalled GOG Galaxy --> no change

Also tried to find out where those libraries come from - it is said that these are part of Visual C++ Redistributable for Visual Studio 2015. Downloaded it and tried to install it --> doesn't work because it says that a newer version of this package is already installed.

I'm really curious what happened. Has someone a good explanation for this and also a working answer?

Thanx in advance.

This sounds like something for the stickied thread:
https://www.gog.com/forum/general/gog_galaxy_official_discussion_thread

And an official support ticket.

All I can guess is that either some of these libraries got overwritten, or were corrupted.
It might even mean registry problems(?) that has lost the path to these libraries.

To confirm, the client was working immediately prior to reinstalling the game?
Could the game have inadvertantly overwritten the C++ runtime libraries with an older version without properly registering the change? Dunno. I'm close to being a moron on problems like this. *shrug*

To be fair, dependency hell affects us all. I've tried proposing solutions, but no one likes ideas that come from a peon.

But it includes some irony that a game update destroys the application which distributes and starts the game.

To be completely honest, I've never had a new C++ redist package completely install over and remove and older different package (other than KB patches). In most cases I've seen, they normally install in parallel, don't they?

The last sentence "Now it works, also NMS can be played with VC redist 2017" got me a little confused though. Did you reinstall 2017 again? Or did you mean "Now it works, also NMS can be played with VC redist 2015"?

Nah, what probably happened is the proper package wasn't even installed for galaxy, so it used the system installed version. When a local version gets installed, galaxy finds that version first. Has to do with DLL load order.