Upgrading usually requires an enormous amount of remediation work before it's even possible. Generally you can do it like this - convert to PackageReference sty

Upgrading usually requires an enormous amount of remediation work before it's even possible. Generally you can do it like this - convert to PackageReference style NuGet packages (this one alone may even be a blocker if you have certain unfortunate dependencies which aren't compatible with PackageReference), upgrade all your dependencies to a netstandard2.x compatible version (this is often brutally difficult in a big system and you may have to replace certain dependencies outright), start swapping out DI / Logging etc with the netstandard equivalents found in .NET Core, create a new .NET Core solution file and try to compile your project to see what breaks and fix any remaining issues. Having done this it does work, but it's fairly time consuming and for larger apps virtually impossible without massive buy-in from the business.