Image Style

It's basically an extreme version of the frequency separation techniques on which you can find tutorials. You would use larger radii for the blurs and you may also want to create custom luminance info and color using Image --> Calculations and Apply Image. In contrast to frequency separation you would also smooth out the luminance instead of simply re-applying it for the surface texture. To make this even more stylized one would also use a "blocky" blur like box blur, bidirectional blur, surface blur instead of Gaussian.

Mylenium 

Could you post (part of) the image you want to edit thusly? 

It's a median filter applied to the the channels, then colorized with a bit of simple masking or selective corrections. As so often the real trick is simply to find the right combinations of parameters. If you were to shoot it you'd aide the process by using very uniform, flat lighting.

Mylenium

They don't look real, do they? 

Maybe they were synthesized by AI.  Or possibly began as vectors in Illustrator.

In any case, you could achieve something similar with one or more filters from Photoshop's Filter Gallery.   See below about how to create a painterly effect from a photo.

https://helpx.adobe.com/photoshop/how-to/turn-photo-into-painting.html

Hope that helps.