I did search but could not find this so sorry in advance if I missed it.....

I am a newbie with Kdenlive so this is very trivial I am sure....

In the top left corner of the clip and project monitor there is some grey letters saying NO DC...
there is also the same text in top left of the screen just below the File menu.

I did try some different settings the default DirectX to OpenGL to try that out as that is used in Darktable.

It might have been there all the time but I did notice it first after trying out these settings. Thanks in advance for helping me with this!

Found the answer:

1. just need to go in NVIDIA Control Panel

2. Click on "Manage 3D settings"

3. Click on "Restore" and after Click on "Apply" button...

and its done !