Replacing an exterior screen door footer threshold to close gap

So I’m repairing issues on a home that was damaged in a flood about 8 years ago. A contractor had done all the repairs after the flood but I’ve found lots of corners cut and shotty work.

The door to the basement is in a stairwell below grade, and consists of a wood door and a glass screen door, with an approx 11in gap between them. Below the screen door is a large gap (seen in the first photo), with no footer below the screen door. I’m almost positive before the flood, there was a wood footer here that was mounted to the concrete below the door frame, that closed the gap under the screen door. So I think this footer was damaged in the flood, was removed and never replaced, leaving this large gap for bugs and other critters to enter the basement freely.

Looking at the concrete below the door frame, I can see there are holes where the previous footer was mounted to, that have been filled with foam, and covered with white paint. Also the area below the door frame isn’t completely vertical, the bottom slants inwards toward the house.

So I’m asking what would be the best way to close this gap so the screen door rubber seal can close against it? I have a pressure treated 2×4 that fits almost perfectly below the door and seals against the screen door rubber seal. Would installing a pressure treated 2×4 across the door frame solve this problem? Or is that a short term solution as it would rot out from the water/moisture that gathers in the stairwell?

Any guidance would be very appreciated, I’m not sure if the terms I’m using are correct as well, I’ve had a hard time finding similar issues when searching online.