I was able to migrate a legacy project using .net framework and entity framework to .NET 7 and EFCore relatively easily. EFCore Power Tools was very useful in doing a first draft of model code from the existing database.

If your legacy code uses Entity Framework 6.3.3 or later, you don't necessarily need to move to Entity Framework Core at the same time that you move from .net framework 4.7/4.8 to .NET 6 or 7.