Apple slice preserves

I love apple jam, especially my mother's: neat, thin slices in thick syrup, with an incredible aroma. This year's harvest was exceptionally generous, so we made plenty.
Adjust servings in the full version
We have our own apples from the garden. Unfortunately, I can’t say what variety it is. Very juicy, sour and completely non-starchy.
Pour a small layer of apple slices into the container where the apples will rest. Sprinkle some sugar on top. Then again apple slices and sugar again. Make 3-4 layers.
After 6 hours we see this picture. The apples have lost a lot of volume. Some of the sugar dissolved and went into syrup. Gently mix the future jam, trying not to damage the apple slices.
After another couple of hours we see that there is even more syrup. Apples literally float in it. The sugar has dissolved almost completely. Stir and leave the jam for some more time until the sugar is completely dissolved.
When the sugar has completely dissolved, put the jam on the stove. Fire is above average. Let it boil actively.
Reduce the heat and cook the jam at a constant boil for about 40 minutes. Don’t forget to stir while drowning the apple slices in the syrup.
The jam is ready when most of the slices become transparent, and if you drop a little syrup on the saucer, it will not spread.