Over the past decade, from the early GTK3 days, the "Broadway" backend has been around to support rendering GTK interfaces into HTML5 web browsers. However, this GTK HTML5 backend is not widely used except for demos and other toy-level applications, and distributions such as Ubuntu and Debian do not provide Broadway support for the newer GTK4. However, that's changing with Debian and Ubuntu 22.10 this fall.
Ubuntu 21.10 and 22.04 LTS do not provide support for the GTK4 Broadway backend, but Ubuntu 21.04 does provide gtk4-broadwayd. Upstream of Debian, they disabled it due to an apparent lack of usage. When GTK 4.4 was uploaded to the archive, the notes read:
Please disable the Broadway (HTML) backend as it is unclear if this is used in practice. If we disable it now, it won't break the ABI if asked to enable it later, but if we enable it now, we have to keep it enabled indefinitely.
So, who is actually using this GTK HTML5 backend? For at least a few users so far, the developers of the instant messaging app Pidgin rely on Broadway code to run their unit tests. Cambalache and Deckard are also using it.
▲ Cambalache
Cambalache is a Rapid Application Development (RAD) tool for GTK 3/4 with an MVC design and a data model first approach. Deckard is a web-based Glade runner.
Insufficient GTK4 HTML5 Broadway support has now been resolved upstream on Debian and in the upcoming Ubuntu 22.10. Back in October of last year, there was a bug report about a lack of Broadway support affecting Cambalache .