After Dark 4.0 Screensavers work just fine on Windows 10 (Windows 11 too actually). However, the older screensavers "After Dark Classic" or "3.0" do not.
The reason for the difference is that After Dark 4.0 screensavers are 32 bit and the earlier ones are 16 bit. Microsoft has disabled 16 bit support by default pretty much since Windows 7.
Running After Dark 4.0 on Windows 10 (or 11) Without Installing
Copy the "Engine" folder from the installer to your computer
Place the "AD40" (aka After Dark 4.0) folder inside the "Engine" folder on your computer
Add the path to the "Engine" folder to the registry
[HKLM\MACHINE\SOFTWARE\WOW6432Node\Berkeley Systems\After Dark\4.00]
"Path"="C:\\Users\\[your username]\\[engine folder]"
Add the path to the After Dark 4.0 Screensavers to the registry. (Note: This path is assumed to have the path from Step 3 above added to the front of it.)
[HKEY_CURRENT_USER\SOFTWARE\Berkeley Systems\After Dark]
Tell After Dark which screensaver to use. This can be any ".ad" file in the After Dark 4.0 folder
[HKEY_CURRENT_USER\SOFTWARE\Berkeley Systems\After Dark\Folders]
"After Dark 4.0"="Bad Dog!"
Run the screensaver by double clicking the
AFTERDAR.SCR file. (Or install the screensaver by Right clicking on it and selecting install.)
.scr files are actually
.exe files. So, if for some odd reason you need an
.exe to run After Dark just rename
afterdar.exe and run it with the option
/s. That will behave exactly the same as double clicking the
As @roger-c-rocha's excellent answer points out there are also additional control options for each screensaver.
Running all of After Dark on a VM
While Windows 10 (or 11) cannot natively run older After Dark screensavers (without basically unsupported hacks), they can run them just fine in a VM. After Dark 4.0 came out in 1996. So, Windows 95 is able to run all of After Dark including the classic ones, and it turns out that these days Windows 95 will even run in your browser. (That's right After Dark on your Cell Phone Web Browser is completely possible.)
Until someone gets around to putting the Windows 95 VM with After Dark online (Hopefully somewhere like archive.org) My recommendation is to use this cross platform Windows 95 VM, and follow their instructions to install additional software (aka your copy of After Dark). Or if you need better speed this less user friendly Windows 95 install on DosBox works great.
At least for me Lunatic Fringe was the only screensaver I could not get to properly function even in the Windows 95 VM. However, it turns out that there is a project to turn Lunatic Fringe into a browser game. Enjoy playing it.