Backstory: There are some gaps around my apartment doors I'd like to fill, most notably a diagonal gap at the top of the main door, as shown in the photo. I own the apartment, not just rent. Replacing/restructuring the door/frame entirely for a perfect fit would be the ideal solution but meanwhile I want a quick fix to cover the gap, primarily to prevent the smell of secondhand smoke from smoking tenants entering my apartment, which occurs regularly as they smoke at the front door of the building close to my apartment. Any sort of padding I place in this gap such as weatherstrips fall out with continued use of the door. I wanted to screw on an upside-down door sweep but the metal door is not very accepting of my cobalt drill bits, as you may be able to see in the photo.
TLDR: How would you fill/cover this gap and fix the sagging door? Weatherstrips fall out and door is unfriendly to drilling.