After searching forever why this issue occurs, here’s what I figured out.
There are quite some wanna-be-solutions around the web for this error, like editing the registry, changing file permissions and so on, but they all do nothing for the actual real problem. Forget and don’t bother with those, because if running the launcher as administrator still doesn’t fix the issue, then none of these will.
The solution to this is actually REALLY simple, in case you have installed Epic Games Launcher on a different drive or folder than the default one, as many developers may have. This one will solve the issue:
tldr; Create manually a folder “C:\Program Files (x86)\Epic Games”. Now try to install it, it should work! You may need to run the EpicOnlineServices.msi file manually instead through the launcher.
Yes, all the installer is having an issue with is, that it cannot install this parent folder on it’s own … seriously… nor will it pickup to the correct location of the Epic installation folder to install there. Dev work at it’s best 