It is there in my AC21 INT version, as you can see it in the screenshot.
If it is not there for you, you can try to create it. You will have to right-click on the right side, and use the "New > DWORD (32-bit) Value" command to create the value and give it the name "KeyMode Shortcuts".
I think after doing this an quitting the Registry Editor, you will have to restart ARCHICAD.
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AMD Ryzen 1700X CPU, 48 GB RAM, Nvidia GTX 1060 6GB, 500 GB NVMe SSD
2x28" (2560x1440), WIN10 PRO ENG, AC20-AC26
Loving Archicad since 1995