You answered your own question.
LEGACY GPUs are not updated with new drivers. If you want a new or the latest AMD Drivers then you need to install a AMD GPU that is still supported by AMD and not considered to be LEGACY (Old and Non-Supported).
If you are referring to the AMD BETA driver from 2016, that is the last and final driver for your type of GPU card and architecture (Non-GCN).
Your only hope is if Microsoft creates a new driver for your legacy AMD card and can be downloaded thru Windows Update. Or you can check the manufacturer of your legacy GPU card and see if they have an updated Driver. Mostly likely they won't.