They're pre-generated by Microsoft. There's a list in HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID you can use to try and find new ones. They've also been document

They're pre-generated by Microsoft. There's a list in HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID you can use to try and find new ones. They've also been documented online for at least a decade, so you can save yourself the trouble. Very few of these CLSID folders are actually useful to have somewhere. An interesting, but underused, feature of Windows is that applications can actually register CLSIDs like these and host their own special "explorer" panels.