Non-RTX Optix Viewport DeNoise

1. That's how LTS software work. If you don't like the limitations of LTS, or don't want to wait for the next stable release when a new feature you like is out, the solution is simple : don't use LTS nor stable releases, use dailies instead. That's what they are fore, and there's no point dev-wise to jam in everything new as soon as possible in a stable, that's actually a terrible thing to do asking for disaster, especially for a LTS.
2. OptiX support is now enabled on all NVIDIA GPUs that support it, which is Maxwell or higher (GeForce 700, 800, 900, 1000 series)

That feature was added by an Nvidia developer and beside that viewport denoise with GTX cards is not fun. Dont expect wonders.