Hello,
sorry for the late reply. The Ghostscript included in PDF24 is a private copy: PDF24 installs it in the subfolder gs of its program folder, uses it only itself and updates or removes it together with PDF24. It is therefore not registered as a system-wide Ghostscript installation, and the key HKEY_LOCAL_MACHINE\SOFTWARE\GPL Ghostscript\<version> is not created.
If another program needs Ghostscript, please install Ghostscript with its own installer: https://ghostscript.com/releases/gsdnld.html
Since version 11.31.0, PDF24 can use such an installed Ghostscript as well. In the PDF24 Settings on the page Components you can set Ghostscript to Installed system version. You can also deselect the bundled Ghostscript in the PDF24 installer; with the setting Automatic PDF24 then uses the installed version. This way only one copy of Ghostscript is on your PC.