To create a Grainy matte effect in lightroom , you have to

☛ Go to “basic” section of the develop module

☛ Make changes like shadows, clarity or saturation if it requires

☛ Now go to the “split toning” section in the develop module and make the adjustment to Hue, saturation, balance, hightlight etc.

☛ And at the last we have to add grain, you can adjust the option like Amount, Size and Roughness