There is no urgent need to repair. I am unsure what the steel, if that is what it is, is doing there. Is it a plate, or the 3rd pic looks like it was an angle? The only thing I can think of is a DIYer wanted a protection for the garage slab edge (like for a loading dock) prior to pouring a driveway.

There should be an expansion joint between the outdoor slab and the interior slab to allow movement. Lacking one, and maybe being connected somehow with the steel plate (maybe welded studs?) looks to be causing movement and cracking lengthwise along the interior slab. There may also be no foundation under the garage opening portion of the slab (I hear common in parts of Canada).

The last picture of the spalling parge coat is because there is no vertical gap between the slab and wall parge, so the slab moved up and knocked off the parge.

I've learned yet more new terms: parge coat and wall parge! Thanks, 3onthetree.

A concrete contractor is the one you would call for the slab. Doesn't have to be a foundation contractor, just one who does "flatwork" (many larger companies do both). They would sawcut a parallel line to the crack and remove guessing 16" or so (e.g. 6" repour would be too skinny). Re-compact the existing base where they demo'd. Then they would drill in for rebar dowels so the new 16" wide repour would not move vertically compared to the old slab. The driveway side edge may be savable depending on how clean the steel comes off. If not, same process.

If the parging/stucco finish is aesthetically fine with you then just paint and cut a groove to separate it from the slab (oscillating tool or disc grinder). Or many handypersons could reparge if a lot more spalls off.