Not specifically about C#, but about something that is also on the radar of people who is developing LoB apps with .NET which is Domain Driven Design. The book by Eric Evans is the bible on the subject, but I also find it very abstract and hard to grasp with no prior knowledge and lack of concrete examples.

Applying Domain-Driven Design and Patterns: With Examples in C# and .NET is a bit old, but still a good resource on how to implement some sort of DDD.

https://www.amazon.com/Applying-Domain-Driven-Design-Pattern...