I don't think moving from legacy .NET Framework to modern .NET is the issue here. I have a web API application that has moved from .NET Framework 4.5 to .NET Co

I don't think moving from legacy .NET Framework to modern .NET is the issue here. I have a web API application that has moved from .NET Framework 4.5 to .NET Core to .NET 5 and just updating for the newer framework has been the simplest part of each upgrade. The real problems come with the changes to the ASP.NET libraries and the changed expectations regarding how such applications are built. This push towards the "minimal APIs" for .NET 6 may be great for trivial or just-bigger-than-trivial projects but it starts falling apart whenever you have something more complex. The setup class system of older ASP.NET editions, while decried as boilerplate, actually makes it easier to manage the configuration and structure of larger web app projects. I don't expect to ever move any of the ASP.NET projects that I work on to use these minimal APIs, and I expect that any new projects will be quickly adapted away from them out of the new project templates out of Microsoft.