It may be worth glancing at this more detailed answer that discussed how aluminum rims were constructed. But in brief, aluminum rims are first extruded in a flat bar, then they’re cut and rolled into hoops, then the ends of each hoop are joined somehow.
One method is to simply pin the ends together without smoothing out the joint. Your rim was built this way, and you’re looking at the seam where the ends were joined. Basically, this is there by design. Look in the corresponding location on the other rim and you should also find a seam.
On higher end rims, the joint is usually welded together and the weld is sanded down. For practical purposes, I believe that the advantages are mainly cosmetic. On pinned rims like yours, you might sometimes feel a bit of a pulse when braking (assuming rim brakes, which you have) when the brake pads pass the seam.
If you hit an obstacle, a more common failure mode would be for the rim’s bead hooks to get dented or to buckle. Rims that crack are more likely to do so around the spoke holes. If the rim cracked so as to look like a seam, I suspect the crack usually won’t be straight. If you can’t find on your bike’s spec sheet that your rims are pinned (may not always be obvious, including on the rim manufactuer’s site), this is one indicator I’d use to differentiate a crack from a pinned rim. Also, a crack may not propagate all the way through a rim, and you can check the other rim to see if there’s a seam in the same location. The photo below, from a different question, looks like it could be a crack rather than a rim seam.