I did! As a high school project. Literally, in high school, one of our assignments was to build a GUI that could make basic HTTP requests (GET and POST, and I think PATCH or something for extra credit) and display the result “nicely.”

Obviously not as full-featured as Postman or Bruno. But this is not something complicated or difficult or novel. My high school teacher had been using this as an assignment since the mid-2000s.