You're all wrong
Look at the pic. the B tension screw isn't the issue here.
On the mech hanger on the frame, there is a tab for the B tension screw to push against. On this mech, the b tension screw pushes against the derailleur itself; so...
In the pic you can see the tab (it's silver, behind & below the top mech bolt). The top mech plate has a stamped tab of it's own that should be behind the hanger tab, but it's in front of it.
So, to fix; Undo the top mech bolt, rotate the plate so that the mech tab is behind the hanger tab and do the bolt back up.
You're welcome