@KostasPap 

If you are talking about restricted mode within the YouTube app, that is done within the YouTube program and doesn't involve the AX50: https://support.google.com/youtube/answer/174084?co=GENIE.Platform%3DAndroid&hl=en

Under the parental controls of the AX50, you would be able to block access to YouTube. 

As you are setting up the filtering options for the profile go to Apps/Websites, and as you type out YouTube, you will see it listed. Select that, and then YouTube will get blocked for devices on the profile. 

@Tony Thank you.
The word i should use is "enforce" youtube's restricted mode.
So, i will rephrase the question better.

Is there a way to enforce youtube's restricted mode at parental managed devices despite apps settings ?

@KostasPap 

Unfortunately no, the two services work independently of each other.

@KostasPap 

Cannot understand why it has to be restricted?

Hey! When I installed parental control on YouTube on applications, I also could not figure out how to do it for the first time. It was challenging with the TV. Children often watch YouTube on TV, so I immediately decided to set parental controls. However, the first thing I needed to do was activate YouTube correctly. While looking for a solution to the problem, I came across https://sites.google.com/view/activateyoutub/, where I found some helpful information. In the end, I just initially set parental controls on my YouTube account. Since the account is shared, parental control was automatically activated everywhere. Now I don't have to worry about what my children are watching.