Last year, Nvidia launched a premium streaming category at 120Hz or 4K for its GeForce Now platform. Both options had limitations; for example - streaming in 4K quality could only be obtained on Nvidia's Shield consoles and devices. Now, this is no longer the case because 4K streaming can be obtained by all PC players.
That sounds great, but with the caveat that 4K streaming games are locked behind a $ 20 monthly or $ 100 subscription for half a year. It can also be used only with the native GeForce Now desktop application, as web/browser options remain limited to 1080p quality.
In theory, you don't have to have a 4K monitor to stream games in 4K, the image will adjust to lower resolutions. The only limitation is that with 4K quality you can stream games up to 60Hz. The 120Hz option, with better responsiveness controls, remains reserved for 1080p image quality.