Secure .NET Upgrade & Fixes

My production C# application currently targets .NET Framework 4.8 and has started to show its age. I need it migrated to a supported, more secure runtime (ideally the latest LTS release of .NET), with every dependency updated and any obsolete APIs refactored... (Budget: ₹37500 - ₹75000 INR, Jobs: .NET, .NET 5.0/6, .NET Core, API Development, ASP.NET, C Programming, C# Programming, C++ Programming)