Developing modern, responsive frontends in .NET can be challenging due to evolving UI frameworks, performance concerns, and cross-browser compatibility. Developers use Blazor for full-stack Dot net development but face issues like initial load time and WebAssembly limitations. For scalability, frontends are often built with React, Angular, or Vue.js, requiring seamless API communication with .NET backends. State management and responsive UI/UX design require extra effort. Using Progressive Web Apps (PWAs), lazy loading, and client-side caching optimizes performance. Ensuring compatibility with mobile devices requires adaptive layouts and UI testing with Selenium or Cypress.