If the behavior is coming from academic instruction that isn't at an appropriate level of rigor for a student, the fix would be to provide appropriately rigorous instruction. Has the school done an FBA? A BIP/PBSP needs to be based on data and an FBA is where this data comes from.
I'm not sure what state you are in so I'm not sure what the rules are on how gifted has to be done. I'm in PA & GIEPs go from K to 12 even though the formal gifted program in many schools doesn't start until 3rd grade.
I do have a suggestion for homework. Modify it to his level. If the assignment is addition of single digit numbers, find a worksheet with double digit addition or change the one he brought home and have him do it and hand it in. Write a note that he was bored and uncooperative with the assigned homework, so you modified it. This also provides data on how mismatched his ability is to the work the class is doing.
If you feel your child needs sensory breaks and enrichment, figure out what the school needs to do to come up with data on that being the need so they can tweak the IEP so he has the right support. There are evals for social skills. Has any been done?
I'm also thinking that this might not be ADHD & anxiety. My oldest was like this - got an ADHD diagnosis in kindergarten. As it turned out, she's on the autism spectrum. She was diagnosed with Aspergers in 7th grade. This was changed to autism level one when the DSM 5 came out. She's 2E. Very bright - had a GIEP. Communication skills & social skills were low. It's a hard combination to deal with. The school saw the intelligence but not the deficits. She finally got an IEP at the end of 8th grade.