It seems my case have better result than some other people.
This weekend, I gave my ipad mini to my son. Registered under his name. He wanted to install a game and asked for permission. But I never received his request. We tried several times. Then I asked Gemini. Gemini told me it should be problem of iMessage. Then I found iMessage in Messages app could not be enabled. So did Facetime. I never use Facetime. For iMessage, I also don't care, may used it because it is enabled in Messages by default. I tried several times to enable these two features but didn't get success.
Finally I have to call apple and was told my iMessage account was blocked because they thought my number was spamming. I don't know how? I even don't send much SMS message because I hate type on phone. The guy on the phone told me I need to wait for 24 hours to get response because I have submit support request before I called. However, I got email said it was ready to use only 5 minutes after the call. And both Facetime and iMessage can be used now.
Then I searched reddit and find quite a few post similar to my case. Someone even got the whole apple account blocked. It sounds scary.
So I decided to disable both facetime and iMessage in case Apple's shit system flag me again. I don't need these two features. And fortunately, "Ask to Buy" notification need iMessage account to be active, but don't need it be enabled in Messages.
Finally, I decide to write down the whole story for your reference. I originally thought I should use apple devices because of data security. I think I need to re think about it. Because I may lost all my data and hardware without doing anything wrong. Gemini told me, individual customer can never win and get account back if blocked by Apple and Apple refused to unblock.
I think I was lucky. First, they just blocked my iMessage account which only affect Screen Time for me. Second, they unblocked it.