Migrating legacy .NET Framework applications to .NET Core or .NET 6+ is challenging due to compatibility issues, outdated dependencies, and architectural constraints. Older applications often rely on Windows-specific APIs, deprecated libraries, and monolithic structures that need refactoring. Modernization requires rebuilding UI components, rewriting business logic, and ensuring seamless data migration. Tools like Microsoft Porting Assistant, dependency analyzers, and Azure Migration Services help ease the process. Implementing microservices, containerization, and cloud-based solutions ensures improved scalability, maintainability, and performance. Dot Net Development extensive testing, do***entation, and training are necessary for a smooth transition.