Grain Merge like Gimp

I’ve been applying Gaussian blurs with Grain Merge and monochrome layers on color images like what is shown in this video: https://www.youtube.com/watch?v=QbWghBFQ9Bo&t=154s

I am wondering if there is a way to do this in Darktable. I was hoping I could achieve a similar effect with a Low Pass Filter but so far, no luck.

Any suggestions would be appreciated!

Thanks!

Kev