Attiny13a LM35 and pot 10K affect each other.

Sorry, but I don't understand what you mean and why I need this power source, cause I'm not going to dim 230V I'm dimming 12V.

No it is a power LED, we need to know what sort in order to give you specific advice as you don't seem capable of understanding general advice.

You say you are dimming at 12V but you should not be unless the LED is more than just an LED but has some sort of current control built in. You should be dimming at the forward voltage of the LED at the current you want to give it. That is likely to be around 4V. That link was for the sort of LED driver you need. If it is not the sort of driver you want then you have to look closely at the sort of LED you have and plan your circuit accordingly.

So post all the details you have about this LED and a link to where you bought it from.