If you have an older NVIDIA GPU, chances are you've been using the 340 legacy series. Well, NVIDIA have said that it's no longer getting updates. This does not affect any of their modern GPUs, just to be clear on that point.
The 340 legacy series is the newest driver that supports NVIDIA GPUs from the GeForce 8 Series from 2006 up to the GeForce 3xx series (rebrands of the GeForce 200 series) from 2009. We're talking GPUs that can be well over ten years old, so it's only natural their support had to end at some point. NVIDIA did recently give it one last update, with the 340.108 released back in December 2019 which boosted compatibility with newer Linux Kernels so hopefully if you're still on it you will be good for a little while.
As for the 390 legacy driver, which is the last that supports the Fermi series from 2010, NVIDIA will support that at least up until the end of 2022. No new feature support though only updates for Kernels, X server and critical issues.
For info on NVIDIA's Linux driver support time-frames, see this page.