Small stoops are often solid concrete. Yours may be so with a rock facade and a cap. There is no way to tell though. You could try to fix this by digging away the soil from the low side and using a lever and fulcrum to lift the low side or corner. At that point blocks could be place beneath the stoop so it is at level when it is lowered back down. But, concrete is heavy and lifting (even with help) might not be doable. There is also the possibility that the stoop could be damaged during the lifting. This is true even if a professional company does the work.

You need amudjacker.

Those stop sign pavers haven't been popular since the early 1990s so I assume this is a 30+ year old install? Given the damage evident near your threshold, I would use this as an opportunity to pull the whole thing out, assess the siding and sill plate for rot ($100 says there's no way that was appropriately flashed), and rebuild the stoop. Those are great looking pieces of stone btw.