>> AC6 should write in Flash by default, shouldn’t it?
Yes, it is the case
>> I will check tomorrow signal NRST on scope. As far as I remember I did it. I can capture reset process.
>> What do you want to seen in it?
Just to verify if the mcu is held under reset or not
any way, you can launch your application in standalone mode, then try to connect to your mcu without reset (hotplug mode) using st-link utility, then read your program counter register (menu > target > mcu core). That will give an idea of what is going.