VR. Tried a VirtualBoy back in the 90s, then those VR glove things, then eventually an HTC Vive and Oculus Quest. They were all cool and fun for a few hours, but having a sweaty heavy thing on my head quickly got tiring. And the games were generally crap that focused more on an "experience" than a gameplay; they felt like barely-interactive movies rather than the nuanced and complex gameplay that's usually on PC. Then Apple tried to take it the ultra-luxury route and that was an even bigger turnoff. I think by this point I'd only be interested in some barebones monitors-in-glasses for watching movies or doing work on, none of the other unnecessary stuff.
--------
Also, home assistants. Alexa and Google Assistant seemed to hold so much promise at first, but they're still so bad a decade later, the third-party ecosystem is awful, and both companies seemed to have completely given up on improving them at all. Maybe the AI boom will revive interest in them at some point (with a natural language to API layer), but I guess there's just no money there, so probably not...