No, the scaling is definitely done by the applications. I don't know how they do it, but it works. I don't think it is possible to avoid having lines "in betwe

No, the scaling is definitely done by the applications. I don't know how they do it, but it works. I don't think it is possible to avoid having lines "in between" pixels when using fractional scaling. The physical pixel grid simply does not always align with the one at "100%" scale. I specifically bought the 4K monitor to get crisp text rendering. Upscaling from 1080p (e.g. what XWayland does) is very noticeable to me. I don't see any difference between native Wayland fractional scaling, and setting Gnome to native resolution (except for the tiny UI elements).