https://www.reddit.com/r/webdev/comments/mkzofs/are_there_any_gui_based_website_builders_for/
Any GUI programs to create and edit web pages (.html files)?. 7 ... Online website builder that allows source code download. 39 comments ...

https://anvil.works/articles/python-gui-builder-web
Anvil is a free Python-based drag-and-drop web app builder.

https://www.totaljs.com/uibuilder/
UI Builder GUI Designer. Total.js UI Builder is adapted for creating UI applications for various cases like classic web applications, dashboards, flowboards ...