Using php + sql and maybe a little javascript is generally an OK-ish method that has few strings attached and runs on anything. However there are a lot of modern frameworks that let you do a lot more stuff. There things like django, firebase, blazor, asp net or whatever but what FOSS equivalent to this “next gen” web development stuff should we be using?
For rapid development of web applications, you should probably use a web framework in a high level language. Popular examples of such web frameworks: Django (language: Python) and Ruby on Rails (language: Ruby). These frameworks have huge communities behind them, lots of documentation, and lots of educational resources available (such as books).