Sounds like my teen son, in terms of challenges. Tho was diagnosed ADHD/ASD in 4th grade.
DBT helped for a but was not the most useful as he got older. DBT eventually felt like someone was telling him what to do and how exactly to cope, while also showing disinterest in the specifics of what actually was happening in his life and upsetting him. That was a bad mix, and resulted in an irritated, therapy-resistant kid.
Anxiety meds were most useful intervention (took the edge of the constant negativity and rumination). Also he eventually returned to regular talk therapy as a HS junior with a therapist that works with adults, who treated him like an adult, which he much preferred and was willing to go to.