If you open a Writer document using the gtk3 backend on Wayland, it is possible to scroll smoothly throughout the document using the touchpad. It is also possible to zoom in and out using pinch to zoom. Even when you use the gtk3 backend on Plasma 6.2, smooth scrolling works fine, as well as pinch to zoom... it also works on Gnome and Cosmic. However, on Plasma using the kf6 backend, smooth scrolling and pinch to zoom do not work. It would be nice to implement these features for kf6 as well.
For pinch to zoom, I can confirm it works with the touchpad for gtk3, but not qt6. Last year's commit efadd5210e56ba67f1b040dff4972fead6a56131 Author: Michael Weghorn <m.weghorn@posteo.de> Date: Mon Aug 14 08:10:21 2023 +0200 qt: Implement pinch/zoom gesture handling implemented some pinch to zoom handling, but I only tested it on a laptop with a touch screen back then (and the laptop I'm using now doesn't have one), not with a touchpad. Do you know any Qt/KDE application that does support pinch to zoom using the touchpad? For smooth scrolling: Can you please be more specific on what the expected behavior (with exact steps you take) would be, maybe with a screencast demonstrating it with gtk3? Version: 25.8.0.0.alpha0+ (X86_64) / LibreOffice Community Build ID: 059e695005b7eb500058f8c1c6cf83eb92dad20b CPU threads: 32; OS: Linux 6.11; UI render: default; VCL: qt6 (cairo+wayland) Locale: en-GB (en_GB.UTF-8); UI: en-US Calc: threaded