@o_lampe
I found the solution! The problem was that I didn't have enough experience in basic electrical engineering.
I needed to use the GPIO port, which supports PWM, to control the servo. However, I took only the "io4.out" wire from the GPIO port.
When I connected the GND contact in the GPIO pad with a "-" 5V power supply with a separate wire, everything worked right away!
Many thanks to everyone for participating!
I think that this problem might not have happened for me if this moment had been described in more detail in the documentation on connecting servos.

@o_lampe
I found the solution! The problem was that I didn't have enough experience in basic electrical engineering.
I needed to use the GPIO port, which supports PWM, to control the servo. However, I took only the "io4.out" wire from the GPIO port.
When I connected the GND contact in the GPIO pad with a "-" 5V power supply with a separate wire, everything worked right away!
Many thanks to everyone for participating!
I think that this problem might not have happened for me if this moment had been described in more detail in the documentation on connecting servos.

@Phaedrux
Thanks for the quick response.
However, it didn't help me, apparently I have little experience.
I am using a Duet 3 Mainboard 6HC (v1.01a) and an external 5V power supply.
Accordingly, the plus and minus servos are connected to an external 5V power supply. I tried to connect the signal wire of the servo to the contacts "io4.out", I tried to connect it to "out8", but the servo still does not work.
P.S.: I have tried all the ways that the author of the original topic tried.

Re: Help to config Servo MG995 for Duet3 6HC

I join the question: How to connect the second MG995 servo? I have a similar task with the author of the topic: I need to connect 2 servos to the Duet3 6HC. Please help