Hello Suan, welcome to the Microsoft community, I'll be happy to help you today;
I understand that you want to disable family security in Windows 11;
You must be logged into the parent's account;
Access the link:https://www.microsoft.com/en-us/microsoft-365/f...
Click Sign in to Microsoft Family Safety;
Remove all permissions from family members you own by following the steps below.
Click Manage my minor's profile information and locate your family member.
Select Withdraw consent for the child's account.
Once all consent has been withdrawn, select Leave family group;
Source:https://support.microsoft.com/en-us/account-bil...
Hope this helps, see you soon!