We must first determine what we mean by the problem. Because light will not stop spreading. The more interesting question is how far away we can see the reflection of the laser pointer under ideal conditions. In complete darkness, when it shines on a white surface, we can see a <5mW 650nm laser from 500-1 km away. The divergence will make the projected point 1km away become a large point with a diameter of 20-30m, and it is very weak. The green laser pointer of the same power is visible from 4-5 kilometers away.
You heard the truth. It will keep walking, keep walking, until it hits something. It will also hit something during the journey. Air is a thing. Dust is a thing. Fluff, water vapor, pollen, flying insects, dust, smoke essence, all things. The photon beam pouring out of the laser object will hit something sooner or later, several at a time, until the last one hits its doom. There is no more laser beam.
The highest average power. Lasers that can provide high average power for tens of seconds at a time are called "High Energy Lasers" (HEL). The most powerful lasers we know are made for defense projects. That laser is an airborne laser. According to news reports, the power of the laser is about 1 million watts, which is twice that.
It has been used many times to destroy unarmed intercontinental ballistic missiles. According to media reports, space green laser pointer have completed their work, including the construction of chemical lasers that may be 5 to 20 times larger than ABL lasers. (I may have been involved in that project.) It has the same purpose as destroying intercontinental ballistic missiles, but from orbit. The project was terminated in 2002 to fund the Department of Homeland Security.
The highest instantaneous power laser. Pulsed lasers have higher levels of instantaneous power. These have been used in fusion research. However, they cannot provide all the energy to melt the missile in a few seconds. They can provide short pulses. The instantaneous power can reach terawatts, but only a few nanoseconds. Such a high power level has a high enough electric field strength to ionize any atom in the beam.