You probably barely remember what Daydream is, or rather was, and no-one will blame you for that. Google launched its VR platform back in 2016 and even introduced its own View headset to the market, which it also updated about a year later. Apps became gradually available for the platform until many of them stopped being updated, or worse, entirely dropped support for Daydream. It was clear Google pretty much abandoned it, but it's now made it official with an announcement.
After officially killing its Play Movies & TV app for Daydream in June 2019, and losing support for Hulu about a year ago, Google is waking up from its Daydream and officially announcing the platform is dead. The company confirmed it will no longer update the software, and that Daydream may not even work on Android 11. Third-party apps could still work with the headset, which isn't available for purchase anymore, but you shouldn't expect these to continue to be maintained either.
Although VR is fun, most people probably didn't see the benefit of buying a headset and compatible apps just for home use, which could explain why Google decided to drop support for Daydream. If you're still interested in VR headsets, you could turn to Oculus, although I wouldn't bet on them continuing to support their products for much longer either.