There may be something going on with your setup before takeoff. The A/THR button should automatically engage when you apply thrust during takeoff. If you have to activate it manually like it appears in your photo, something earlier in the flight may be the issue, or, it was manually turned off. Under normal operations, you do not need to disable A/THR. You would just use managed or selected speed and let the thrust system do its magic.
Since you don’t have it engaged in the photo, and you are using a static thrust setting, you are going to over speed. It appears an inactive thrust system is contributing to the issue. Looking at your FMA above the PFD, you do not have a thrust mode active.