I was several times required to build simple web apps, and it wasn't hard. I used Python, Flask, Jinja2, Bootstrap, and maybe one or two functions from jQuery for AJAX. It was very easy, and I know only Python and basic HTML and CSS. I don't know any JS/TS because I'm a Computer Vision Engineer.

These web apps show tables with data, images with figures, and some controls to request calculations or data from a server. jQuery is used to update the drop-down list according to previous choices.