I saw this photo of african violet leafs and just wanted to ask if it is really possible to propagate them this way. If anyone tried it and if it works
Yes, it works. Use any type of soil that has a loose touch because the plants need some oxygen in it and if it's too compact it will keep only water without air.
Water only when the soil is completely dry, not dry only at the surface. As a personal note, I wouldn't burry all the leaf stem because they are sensitive to overwatering and rot easily.
I burry only 2 cm of the stem and works well. At the lower end of the stem, new roots and a new rosette of leaves will be formed. You can use transparent plastic cups to see better if the soil is still moist in the middle part. Make drainage holes on the bottom for easier management. Don't make drainage holes if you are absolutely sure you won't overwater.