First order of business: this character—Kylie—and her weaponry was created using mods available on Xbox 1 for Fallout 4. The character’s look, apparel, and weapons won’t be available on all platforms.
That being said, the Solar Canon is available for all platforms as it comes from the Creation Club. For anyone not familiar with the Creation Club, it’s a downloadable product available from Bethesda that works as a substitute for in-game microtransactions. The DLCs (I use the term loosely) are purchased with real money unless they’re specifically offered for free of a period of time.
As I mentioned in the video, I believe the writing is poorly executed. And I’m not sure the story itself is well articulated. A bit more time—and a proper editing—would have done wonders for this quest.
Overall, I don’t think this purchased content is worth your money, even if you’re a weapons hoarder. Wait for sale or free. There are enough base game weapons that are more than equal (several excelling) to this purchasable content.