Model lighting problem. Half-block and stairs. It is covered with shadow inside.

I created a staircase, but such a shadow appeared inside (see 1 photo). I tried to turn on soft lighting in the settings, it did not help. I set the getLightOpacity line to 0, the problem went away but the block became semi-transparent. I don't need the block to show through. As far as I understand, parts of the block need to be rendered separately. That is, I need a part (void) circled in red in 2 photos so that it allows light to pass through, and the green part, that is, the step itself, should not transmit light at all. The same applies to the stone slab, so tell me how can this be done? I'm not good at programming and don't know what the code should look like to make it work. There is no such information on the Internet at all. Or are there other solutions to the problem?