The Nvidia support page does note that if you still insist on using a PC with those older operating systems, you can still connect and play on the GeForce NOW service with a supported web browser ...

This special group of GeForce Now members can also upgrade to Ultimate, where they will have the playtime cap, and revert to ...

GeForce NOW taps into the thriving PC gaming ecosystem by streaming games from NVIDIA GPUs in the cloud, this week adding 6 new titles to its library.