People who don’t have children with ADHD don’t realise that the usual behaviour strategies simply don’t work!
I get it OP. Try and find a course, local or online, about dealing with ADHD, it did help me.
DS is now a young adult, but things we’ve done over the years which have helped:
we don’t buy snacks, treats are only for Saturday and or Sunday and they are earned
lots of physical exercise
when behaving well, show a huge amount of attention, smiles, laugh, dance, etc
when calm, show lots of love, strong hugs, so that they feel secure
when not behaving don’t react or give too much attention, any attention even negative is what they want
however, there needs to be a consequence for all type of negative behaviour, it needs to be something you can control, but you need to be very consistent
don’t give your kids crap processed food with sweetners, etc
good luck and don’t give up! I promise you there is light at the end of the tunnel!