1. Anxiety, hyperfixation, irritability, difficulty dealing with schedule changes, mental inflexibility, etc. It is not that strong, but enough to drain me during bad periods. Neither therapy or meds actually helped me, I felt stuck and without a visible way out. A little while my therapist suggested I get a neuropsycological evaluation (direct translation, don't know if the name in actually this in english). And I got a strong possibility (investigating now) of being on the spectrum, altough my "support level" is the lowest (my characteristics aren't that high in ant of the spectrum characteristics. And most of my expereriences seemed to fit in the problems undiagnosed adults goes through.
2. It seems too early to day anything with confidance, but so Far, I feel like I understand the reason behind my feelings and behaviours.

It is called spectrum for a reason, you don't need to fit them all, and could have manageable levels in some of them, but having to compensate in others. As you therapist said, and undiagnosed neurodivergency could be a reason the therapy poor results, It is like they aré following a script that wont work on u.