Hi, i got the same problem with 4.26 in Win10 64.
So i fixed that with this cmd file: UnrealProjectMenuRegistration.zip (1.1 KB)
1.) Download, extract and open “UnrealProjectMenuRegistration.cmd” with notepad or another text editor.
2.) Goto Line 16 and make sure, your install path of unreal is correct. In my case it was:
HKLM\SOFTWARE\WOW6432Node\EpicGames\Unreal Engine
3.) Save it and run it as administrator.
So i dont need restart windows, but its not work - try restart and context menu should work.
Hope it helps! 