Hello, I understand your need for a versatile programming language that allows you to develop applications across multiple platforms from a single code base. Considering your familiarity with C and C++ syntax, along with your requirements, I recommend exploring JavaScript and Dart (with Flutter) as potential options.
JavaScript offers extensive support for web, desktop (via Electron), and mobile (with frameworks like React Native and Angular). Dart, on the other hand, is the language used in Flutter, which enables seamless development of native interfaces for various platforms, including the web.
Both options align with your goals of writing code once and compiling for different platforms. Given their robust ecosystems and community support, they are well-suited for your project, including the development of a web app for a visual DBMS.