Black Hole or 2nd Star
The risk from a black hole coming in our direction is reasonable. But black holes, although having titanic forces within are still in the area of star sizes and the gravitational effects of stars. The really massive ones that are said to be at the centre of all galaxies are moving with those galaxies and we don’t have any galaxies that are immediately in our vicinity and heading in our direction. They do move, but it’s likely that we won’t have anything like this as a threat for millions of years.
If you had a sun size object moving in our direction you would likely know about it as the gravitational forces would show themselves at quite a distance. But even a miss on our planet may have a terminal effect on our sun unless the velocity was such that it would simply miss and not combine with our system.
So, the biggest threat would be that we would lose our sun and most of its power, that is, if we survived the catastrophic effects of the sun and black hole combining. The effects would be similar for a 2nd star hitting our sun, the combination that could cause a massive energy outburst that could fry most of the planets.
At the moment there isn’t another star within 3 light years, and none that seem to be moving in our direction.