This example shows off the builder style, but since gtk-rs is built on top of GTK, .ui XML files are also supported. You can edit .ui files using the legacy Glade editor (with a conversion script), the newer (but incomplete) Cambalache project, or by hand (it's not that hard and this seems to be the preferred way nowadays)

https://gtk-rs.org/gtk4-rs/stable/latest/book/composite_temp...