Glade itself is deprecated, but the UI XML file format it works with is not. Cambalache and Drafting are two WIP projects to replace Glade.
Until then, you can either avoid UI files, write them by hand, or my favorite option: use blueprints[1], a file format that compiles to UI files. For instance, this file[2] describes a form with a folding advanced section, complete with functions to call when buttons are pressed, and CSS class names to apply to widgets.
[1]: https://jwestman.pages.gitlab.gnome.org/blueprint-compiler/
[2]: https://github.com/JMS55/whatthefn/blob/master/res/blp/profi...
