AncientEmo I am so sorry to hear this, how hard for you.
There have been quite a few threads about behaviour on here recently so might be worth reading up a few, started over the last few months, as there is wisdom in there.
I really suggest and second whoever also said it, that post adoption support is needed and is helpful.
Our son came to us at three and is now 10. He had quite a lot of anger issues, being very emotional etc. At about 5 he had a series of sessions called Theraplay, which is a specific kind of play therapy. It was amazingly helpful. I am afraid I am very boring as I mention it on here a lot!
You may need to wait to get it but you want to get on a waiting list for it. You have a budget of money you can spend on therapy for your child or intervention for you child and so I think it is very helpful to find out what options you may be able to get.
Also, please, please make time for yourself. Whether it is a cup of nice tea or a hot bubble bath or walk by yourself. Again, I say this a lot. I think it's so important you refresh yourself.
If you have a partner make sure they are pulling their weight.
Even if you do not have a partner you must have some support. The whole support group thing you must have been covered in your prep and so is now your life support group. They may be people who can look after ds just for a short time so you can recuperate. Or they may be folks who can speak to you by phone or zoom at night when your little on is in bed etc.
You are not going to f him up! Honestly, you are doing your best, and that is great. But you just need some support for him and for you, IMHO.