What kind of metal is safe for DIY BBQ repair?
Best would be a cast iron/steel piece, it would last forever and do exactly same as next item.

Second best would be mild carbon steel, what we call black steel where I come from. It rusts like no tomorrow but it is cheap, sturdy and no surprises.

Stainless is a waste of money, heat over time will both make it brittle and leach mystery compounds like chromium into nearby surfaces.

Galvanized is ridiculous, as propane heat will melt the zinc and it will make a puddle.

Best performance is heat resistant high alloy steel with large portions of nickel, molybdenum and others. What we call "kettle steel" in my neck of the woods. But that is hard to work into shape, difficult to weld, heavy as bricks and thus expensive.