It's fixed for me now.
This issue seems to be finally fixed for me.
It's still broken for me.
I'm also having the same issue.
Did you try this? https://help.minecraft.net/hc/en-us/articles/360042221252-I-m-Getting-an-Error-When-Trying-to-Play-Multiplayer-with-a-Child-Account
I don't know.
It still happens even on the new version.
It's fixed for me now.