Sharing some illustrations from Handsomefrank agency. If you see them, all have dotted / grainy colors.

I've highlighted the thing I want to ask about by yellow color.

It's not limited to one artist. For example, you can see this artist's work also, where in some illustration you would find similar grains or grainy gradient but non-uniform.

Now, I know similar effect can be done using Illustrator Filter > Artistic > Grain or similar filter. I've done the same in one of illustration done by me below (in the main background):

But there's slight difference in between mine and the ones shared above. 1) The grains are non-uniform. Looks like the designer used more effect where he wanted more and less where less needed. 2) He even has used in form of gradient also.

I can do both things like I've done in Teddy, but the grains are too large, and are not subtle. Also they feel different than mine, looks like sand particles spread over layers by hand. I think I like mix of both effects, so I want to learn this techniques also.

So is it possible and convenient to do this in Illustrator? Or you would recommend Photoshop (where there are lot of free brushes available)?

Also I don't want to limit myself to grains only. I want to know about it and learn this technique so that I can try other similar types of grains/effects also.

Sharing some illustrations from Handsomefrank agency. If you see them, all have dotted / grainy colors.

I've highlighted the thing I want to ask about by yellow color.

It's not limited to one artist. For example, you can see this artist's work also, where in some illustration you would find similar grains or grainy gradient but non-uniform.

Now, I know similar effect can be done using Illustrator Filter > Artistic > Grain or similar filter. I've done the same in one of illustration done by me below (in the main background):

But there's slight difference in between mine and the ones shared above (first 2, done by agency). If you observe them: 1) The grains are non-uniform. Looks like the designer used more effect where he wanted more and less where less needed. 2) He even has used in form of gradient also.

In my case, I can do both things like I've done in Teddy, but the grains are too large, uniform (see pink background) and are not subtle. While in the agency's, they feel different than mine, looks like sand particles spread over layers by hand. And is non-uniform also at some places. I think I like mix of both effects, so I want to learn this techniques also.

So is it possible and convenient to do this in Illustrator? Or you would recommend Photoshop (where there are lot of free brushes available)?

Also I don't want to limit myself to grains only. I want to know about it and learn this technique so that I can try other similar types of grains/effects also.