I'll admit, I always forget about the Spellbound quest. To me the coolest one was always the Kold Mirage, but Spellbound has the better reward, oddly. So the result is that I have always done Kold Mirage, despite the fact that most online guides suggest you need to do Spellbound first. Nope.
You can trigger Kold Mirage by either doing Spellbound for Nix, first, or you can do the side mission, "Many ways to skin a cat," where you'll then collect the necessary data shard, at Revere's Courier Service, and kick off Kold Mirage quest. Except the latter did not work for me. So the answer seemed obvious. Either it was a bug, like everyone else suggests, or there's another unknown requirement. I, myself, suspect there is an unmentioned prerequisite, to get both Kold Mirage and Spellbound to trigger, and it makes sense, when you think about it.
Like many, I opened the fridge way early in the game. Almost as soon as I could leave Night City. This is because I remembered Bartmoss from my first play-through and each play through after, I thought I could shortcut it and get some decent cyberware, early, since I now knew of the location for the cyberdeck. I've played through the story 3 times, and each of those additional times? I had this same frustrating experience. The first play through went off without a hitch, because it didn't even occur to me to visit the spot where V's story began, until much later into the game, when I had one of my last few gigs remaining. The Sparring Robot mission. It wasn't until then that I had discovered both Dex's Plan-B pistol and the fridge. Once I opened it Johnny immediately began speaking about Bartmoss.
So, what do you need?
Anyway...you need to have completed Ghost Town, true. However? It is most likely that upon completion of Ghost Town, you're intelligence might be too low. Specifically your breach protocol (not your attributes) and, so, Nix won't even have a dialogue prompt, which many attribute as being a bug. But it makes sense because Nix is allegedly Night City's best Net Runner, who is familiar also in legacy tech...despite the fact that he sells crap for cyberware...but in being a famous netrunner? He probably won't just talk to any "would be" hacker. Therefore, I am about 90% sure you need to have max your breach because that's when it finally kicked off, as, for me? After having tried every single guide out there to unlock either Spellbound, or Kold Mirage, on going through 2 play-throughs? I've always turned up empty-handed.
Kold Mirage finally triggered for me, once I maxed it out at 20, but not immediately. Like anything else in the game, it seems to be time driven, once a requirement is met. I wasn't even anywhere near Bartmoss, nor Nix, when it triggered. I was walking out of the building, after having done one of my last few remaining friendship/ relationship missions, for Judy and Kerry, prior to setting off to meet Hanako at The Embers. The exact mission I had concluded, at the time, was "Off The Leash," for Kerry Eurodyne, which I had done immediately after Pyramid Song. As soon as I walked out of the building and drove up the road, Kold Mirage kicked off. Now this was about maybe 2 in-game hours after having hit max breach protocol.
Once I concluded Kold Mirage, I set off down the road and literally 3 minutes after having left The Afterlife, I received a notification pop-up for Spellbound, and so I had to drive back to Nix, again.