> toolkits do come with full multiplatform renderers with capabilities not too dissimilar to a browser
This is correct. But a menu does not need the entire set of capabilities of a toolkit like GTK4 or Qt6. It might take as much as Xlib or GL, which give you a way to draw simple shapes and text over a full-screen transparent window.
Most importantly, they usually do not include a bunch of things Javascript engines and even mere https clients, at least not easily accessible. (Though e.g. conformant XML parsers are always a hazard. And of course Qt6 does include a JS engine, but hopefully it's a bit more isolated.)
This is correct. But a menu does not need the entire set of capabilities of a toolkit like GTK4 or Qt6. It might take as much as Xlib or GL, which give you a way to draw simple shapes and text over a full-screen transparent window.
Most importantly, they usually do not include a bunch of things Javascript engines and even mere https clients, at least not easily accessible. (Though e.g. conformant XML parsers are always a hazard. And of course Qt6 does include a JS engine, but hopefully it's a bit more isolated.)