Hello Jh B,
The Q&A Assist's steps apply if your account was originally created as a child account.
However, you mentioned you're the organizer with no child accounts linked. If you're the organizer with no child accounts linked and multiplayer is still disabled, your account may be incorrectly flagged, and the privacy settings fix won't work on your end.
In that case, you need to contact Microsoft Support directly at https://support.microsoft.com/home/contact and request a manual review to correct the account classification, with a government-issued ID ready to verify your age.