X-T2/X-H1 120fps is derived from line-skipping the full sensor, moire/aliasing/noise are severe, the video above (and a few similar ones) use heavy grain and aged film effect to cleverly mask those image artifacts. It's a nice workaround but has limited use.
X-T3/X-T30 120fps improved considerably by incorporating weighted pixel-binning and reduced line-skipping (at the expense of 1.29x crop).