CsprojToVs2017 VS IsExternalInit

Yes, probably. Try the guide at https://learn.microsoft.com/en-us/dotnet/desktop/winforms/migration/?view=netdesktop-7.0. I personally prefer the tool https://github.com/hvanbakel/CsprojToVs2017/, but it's a bit more manual.

There are a few tools that can help in the process. Years back I used a tool named Project2015to2017: https://github.com/hvanbakel/CsprojToVs2017. Since then, Microsoft also released a tool: https://github.com/dotnet/upgrade-assistant. There was also this tool but it looks like it has been discontinued: https://github.com/microsoft/dotnet-apiport

https://github.com/hvanbakel/CsprojToVs2017 to convert projects to the new format. This is much nicer in multiple ways: VS doesn’t need to reload the project when it changes, version control changes are much less noisy, you get a Dependencies node in Solution Explorer instead of the old References one, etc.

There is a much better tool for that: https://github.com/hvanbakel/CsprojToVs2017

I've been a bit luckier in that regard, but I'm not sure if your path wouldn't have taken less effort. I use https://github.com/hvanbakel/CsprojToVs2017 (dotnet migrate-2019 wizard) to modernize the projects, then further tweak them by hand. For ASP.NET projects, it's indeed a very difficult road. WebForms outright doesn't exist, and Core is very different from MVC in some areas. https://github.com/CZEMacLeod/MSBuild.SDK.SystemWeb helps somewhat.

there's https://github.com/dotnet/try-convert. Haven't tried it; I instead use https://github.com/hvanbakel/CsprojToVs2017, but I assume the former might be a better choice by now.

I personally used https://github.com/hvanbakel/CsprojToVs2017 to port an existing 450+ projects solution using the old .csproj format to the new one. I had to manually fixup some projects afterwards but overall a good experience.

You can also just reference the https://github.com/manuelroemer/IsExternalInit NuGet package.

init only properties (likely to come up if you use records) - you can either use the IsExternalInit nuget package or manually define the attributes - either way, the feature works perfectly fine

…and a NuGet reference to https://www.nuget.org/packages/IsExternalInit, I can then do public record Foo(string s); and have it build.

You only need https://github.com/manuelroemer/IsExternalInit for that (and to set LangVersion).

Even for .NET Framework code, I tend to use recent C# versions. I reference https://github.com/jnm2/ReferenceAssemblyAnnotator to get nullable support and https://github.com/manuelroemer/IsExternalInit for records, and that takes care of most of the features I care about.

features that require BCL additions. Since you're on the older BCL, those will need to be backported. For example, to use init; and record, you can use https://github.com/manuelroemer/IsExternalInit.