Gap between brick wall and siding?

silicone or perhaps a plastic molding to fill the gap

Use tablesaw to rip a strip to fill gap first then caulk and paint to stain to match

First, check to be as certain as you can that there are no bee nests, water damage, mild or anything else that may need to be done prior to repair.

Fill the inside of the gap with crumpled paper, insulation or whatever seems best just to cram into the interior gap. If possible you can cover that with some wood strips or shims. None of this is structural so you don't need to worry about nailing it in, etc. Just get the gap mostly filled up.

The reason is that the final product to use would be pricey if you fill the entire hole with it. Get some "Great Stuff" (home depot). This comes in a can. You spray it in the gap and the foam will expand, closing it up with a waterproof material that will dry like hard Styrofoam.

Once hardened take a utility knife to cut away any excess. You'll basically sculpt it to look nice. Then paint with exterior house paint.

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They make those black foam insulation tubes just for this. Ck by the door insulation stuff. Find the one that fills the gap tightly then buy weather proof silicone caulk and caulk cover the tube to fill the gap. Caulk comes in Colors or you can paint

I think your best option is to use the spray foam in the can, let it expand and then trim off even. Any good quality exterior caulk such as "DAP" can be painted over if necessary.

Your best option is the way it’s done by the companies that do this to houses the day it’s built. They sell a caulk that is color matched as close as possible to your vinyl siding and or brick. Buy it and run it in there. The structure and insulating materials like house wrap and all of that are already there this is just beautification someone didn’t do it correct the first time. It’s made a little different than regular caulk kind of how roofing material comes in a tube for a caulk gun. It’s in the vinyl siding section of home depot or Lowe’s