> This is outdoors.

It is not.

My complicated plan is to screw a plank onto the wall and mount the striker onto this..

Sorry I broke your brain because I wrote latch instead of striker.

The 2ft plank will disburse impact joules across a big surface so it will protect the sheetrock. And it's 2 ft because you'll find a stud within 2 ft to mount it to.

The plank adds material the strikerscrews can firmly grip. But the width of the added material will make it impossible for latch to catch striker since striker will now stop 1 plank width in front of latch.

So you inversely mount striker so that striker bends towards latch and therefore negates added material.

This is why you picked out plank width same as height difference between striker bend and striker mountpad

Carve out the curvature of the striker mount if you need the catching point to be exactly the same as before.

Add folded paper underneath plank if you need to make outwards micro adjustments to the catching moment.

The goal of the adjustments are to make the weight of the door slam into the doorframe, not the striker.

Rusty screws are not a problem because it's inside. Paper shims will not soak up water it's inside. (OP said it's inside the house and there's carpetted stairs in the picture ffs)

Screws will not snap off since I adviced to adjust the catching moment of striker in such a manner that the doorframe catches the door, not the striker.