Using Ryzen with Vega graphics with shared memory.
KDE 5.
Measuring by nvtop utility.
Simple usage takes ~ 300 - 400 MiB VRAM.
With running browser(s) ~ 700 - 900 MiB VRAM.
Adding tabs in browser increases memory usage.
Usage of HW video decoding occupies additional VRAM.
Previously I thought that 256 - 512 MiB VRAM is good enough.
Tablet PC works with 128 MiB VRAM, but possibly requires more.
ATI/AMD Radeon HD 2900 PRO/XT, some cards from Radeon HD 3000 series and newer are available with 1 GiB VRAM or more.