There is a 9V optocoupler on the 4th leg. The optocoupler is new and working, tested by a probe. There is no other arduino.  Which one is better to buy on ATmega328P or Atmega168P?

Ok, test the Arduino then. Try different HV_EN and HV_FB pins, if default ones aren't working.
ATmega328P has more flash memory and EEPROM storage, so it would be a better choice, IMO.

I tried to repeat HV_EN on D10, the same thing. Thanks for the help. I'll buy a new one, then I'll write.

Hello! I can't do it.
I bought another Arduino nano, everything is the same. I checked the scheme more than once. The DIMM adapter is working, another programmer is reading it. All the elements are according to your scheme. What's next?
I'm using version 20231210, and it's the same with 20230930.

Post a photo of your setup.

You can measure the voltage on the D9 HV_EN at the time of Arduino initialization in the RW_SPD program. I have less than 1 V. on D9 , and in order to open the optocoupler, you need > 3 V.
How do you power the Arduino, via USB or an external source on the VIN?

Mine is powered entirely off USB.

How do you run the RW_SPD program then?

It seems like your VOUT- is connected to SDA or SCL line. If that is the case, your SDA or SCL pin is grounded via VIN- pin, which could be the reason Arduino can't see any I2C devices.
 

 
Check the resistance between SDA/SLC and GND. It should not be 0.