What are some great books that could help me learn to write *modern* C#?
I will mostly work with web and .NET Core, are there books specifically about using .NET Core on Linux?
Essentially, .NET Core has dropped the "Core" moniker. It's just .NET (I tend to refer to it as .NET proper when differentiating between Framework). This change began with .NET 5.0.
If you're starting from scratch, you will want to build everything using .NET now. Do not use .NET Framework unless absolutely necessary. Probably the most common reason you'd be stuck using .NET Framework is because your project is reliant on some driver or library that isn't making the transition to .NET proper. If you're in this situation, you should try to move as much stuff as you can to be on .NET proper and then use .NET Standard, a middle man library Microsoft developed for this exact situation, to allow for cohesion between .NET Framework and .NET proper.
Otherwise, in terms of specific "modern" coding practices? I'd say to pay attention to modern OOP approaches in general. Dependency Injection seems to be used everywhere now. Also, be careful using Reflection. People get a lot done with it really fast, but if it starts being used for more than just attribute inspection and you're doing some crazy shit with it, that's usually a sign of a bigger architectural issue.
Lastly, review LINQ if it's been a while for you. Specifically, understand deferred execution as a lot of people shoot themselves in the foot by tacking on a `.ToList()` and enumerating over a massive collection they shouldn't be enumerating over.
C# has changed a lot, but it's more subtle than the way a lot of other languages have progressed. Mostly just new features that you can survive very easily without. C# 14 is bringing some interesting changes though, but that's still pretty new, so I'd see the release notes on that if you're interested.
The lead indeed rewrote the codebase to .NET Core, but had trouble publishing changes to the server (his current method of updating views, for example, is to copy some files from his local version and overwrite the files on the server). I guess he couldn't do this with .NET Code, so he just reverted back to .NET Framework. To me, it seemed... odd. Surely there's a way to publish changes in easy manner?
For web dev specific guidance it's hard to beat ASP.NET Core in Action by Andrew Lock. Check out Lock's blog too at https://andrewlock.net, it's a great source of new features happening in ASP.NET. He does go into publishing an app on both Windows and Linux, with a decent guide to both. But you'll probably want to read through MSDN docs on that as well, I don't think there's a book that goes in very deep on that.
For generally writing modern C# using .NET, I like Code like a Pro in C# by Jort Rodenburg.
For a quick tour of modern C# features C# 12 in a Nutshell by Albahari is basically the reference guide. 12 is the latest, grab any of them from probably 7 up for a decently modern take.
Reading the release notes of the sdk and/or the MSDN pages used to be a great resource, and probably still is, but it's difficult to find new gems.
My advice is to download .Net 9 SDK because it's now super easy to create a file with extension .cs, put your terminal window next to your code, and call `dotnet run file.cs` and it just works. The compiler will teach you a lot because the errors are extremely easy to follow.
I never bought into books because too many language features have been added in the past years that improve on "old" ways.
The only complaint I have is that Google is still the best interface for navigating the docs. Spamming google over and over. Solving this in an easily greppable way is on my wishlist.
Especially because I see the MSDN docs are rolling out new "Did you want to generate a sample of this? Here's a prompt you can copy paste into Copilot to generate an example: xxxxxxx blah blah"
https://learn.microsoft.com/en-us/dotnet/core/whats-new/
https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/
Can also recommend reading:
https://learn.microsoft.com/en-us/dotnet/core/tools/ (CLI, it's good)
https://learn.microsoft.com/en-us/aspnet/core/fundamentals/m...
https://typescript-is-like-csharp.chrlschn.dev/pages/interme...
> are there books specifically about using .NET Core on Linux
There is nothing particular to using ".NET on Linux" - it just works. Standard Linux caveats not specific to .NET apply.