I had trouble recently installing Epic Games Installer on a new Windows 11 laptop. The installer would load but then it would flash a box saying that this was not a Microsoft application and I should get from the Microoft store or change the settings to allow downloads.
I followed all the help pages from Microsoft, but the settings that it was telling me to change were not there. I followed the text, went into the sections with the icons etc however there was nothing I could see would allow me to change the settings so we could download and install apps from outside locations.
Nothing I tried would work, I worked with a friend and I tried installing Powershell, this would not allow me to install that as well, this is a Microsoft product, this was even more confusing.
The next step was searching for a registry key, this is when we solved the issue. When I tried to load Regedit, it flashed up a box which explained this can’t be loaded, along the lines of needs to be a Microsoft setting etc, I clicked on the link and this then loaded a nice page that explained Windows 11 was running in S mode.
Once I clicked to turn this off I was then able to install the Epic Games Installer.
So if you come across an application you can’t install, perhaps see about disanling S mode.