I have a kid who did exactly the same and we work with his frustration by putting buckets of water with bubbles and find out that it relax him. I know that it’s a spectrum but you can try and hopefully works.

My son started banging his head during COVID. I think there was a lot of upheaval then with changes in routine. I found a good pysychiatrist and he started taking abilify. He was around 8 years old then. He still has a couple SIBs. He likes to jump up and drop to his knees when he is constipated or upset but I haven't seen the head banging anymore.

My daughter would slam her head to the floor we got very good at knowing when that behavior was going to happen then jumping under her. The goal is to let them know you recognize they are angry/ upset buy once she wants able to harm herself most of the head banging stopped. I know it's a battle but your kid gives you lots of signs it's coming just knowing your going to say no helps. I normally don't suggest restraining except with self harm behaviors. It still happens from time to time he bites because he knows it hurts him so in turn hurts you. My husband hated it but I would tell our daughter " you have the right to be angry. I hear you are angry. You do not have the right to hurt my baby because you are angry. " kids in general don't look at situations with outside perspective. You have to show them. By me saying my baby she learned that I will protect my baby. Once the head banging wasn't an option she tried other tactics util she found one I accepted. She claps her hands together and says NAH NAH NAH. I still say you have the right to be angry for xyz let's look at something we can do then it's back to good ole non self harming diversion. It wasn't easy and we got hurt diving under her so her head didn't hit the floor but once the consequence changed and the goal of self harm wasn't met she went on to other things. He is your baby and he needs to know he doesn't have the right to hurt your baby but he does have the right to be angry and express it in a non violent way.

I would def say to stay calm, and give him words. “You are frustrated! Hearing no is hard.” Then quick (or just) 2 or 3 words, then redirect. “That’s hurts, ouchie!” Hold his hand (or head) and redirect. And if he wants attention, give it to him before he asks for it. This will make “no’s” easier to swallow. About communication, ensure with great calm and patience, that you see him and you hear him. And that you will wait for him, as long as it takes. There is no learning happening when he’s in these outburst moments, he’s communicating to you that he’s out of control and hurt inside. These moments will pass. As a parent I suggest a little bit at a time. “I see you. I hear you. I love you.” When my son head butts, I ask him if he wants me to squeeze his head. Usually, he does. When he’s disappointed about something, feeling left out or not heard, screaming and throwing things, he can usually get over it fairly quickly with me explaining what happened (showing you see him) and then redirection to a preferred activity or sometimes all he wants is true connection. Then we can snuggle or keep talking. Sounds like you’ve recognized his triggers, now it’s working through each one. I don’t think there’s one blanket answer for all SIB. But I do know that it’s heightened when there’s 3 or 4 triggers happening all at once, then the explosion. Break it down into manageable chunks, and do little by little.

Is he considered non verbal ?
Have you tried and AAC device. My son would self harm
Until he was able to get some
Language. First sign language a few words to help understand what he needed and then an AAC device. He has language now but sometimes he can’t get it out so he still
Has his AAC device