Hey Avery!
Nice to meet you! I'm Darhyl, an Independent Advisor.
Based on your description, your account may have been the Organizer in your Microsoft family however, the system can still detect that your account is only a Child account due to its registered age upon creating the account.
To fix this, kindly create a new Microsoft adult account with a new email address on account.microsoft.com
Note: Ensure that the adult account's birthdate is registered as 22 years old or older.
Once you're done, using your child/main account, add the newly created adult account to your family as an "Organizer" then using your adult account, remove the child account from your Microsoft family and re-add it as a "Family Member"
Note: It is important that the adult account is the "Organizer", and your child/main account is the "Family member" to make this work.
Once it is done, you can proceed using the adult account to manage your child account's privacy settings according to the official Xbox website: https://support.xbox.com/help/family-online-saf...
"Sign in to the adult/Organizer Microsoft account at Xbox.com.
Select the adult account's gamertag, and then select the More actions button (…).
Select Xbox settings, and then select Privacy & online safety. Because you’re accessing sensitive info, you might have to enter your password or PIN.
Select the gamertag of your main/child account that you want to manage.
Select the Xbox Series X|S, Xbox One, and Windows 10 devices Online Safety tab or the Privacy tab.
Review your current settings and update these options as "Allow":
> You can play with people outside of Xbox Live.
> You can create and join clubs
> You can join Multiplayer matches
> You can add friends.
Submit to save your changes.
Then select Submit to save your changes.
Note: You must select Submit at the bottom of the page before leaving or switching to another tab. If you don't submit the changes before you move to the other tab, your changes won't be saved."
Wait up to 24 hours to make sure the changes will be applied.
Then have your main account sign out and re-sign in to the Microsoft Store and Minecraft Launcher to see if the multiplayer works.
Thank you for your kindness and understanding! Please let me know if you need anything else.
Best regards,
Darhyl