[PJDK]

Speaking as someone who has led teams in small startup .net companies.

At your level I'd not really be thinking too much about specific C# skills, I'd just expect you to have them. Books wise I'd be looking for texts with a wider application. Pragmatic Programmer, Clean Code, Code Complete. Jeff Atwood maintains a good list https://blog.codinghorror.com/recommended-reading-for-develo.... A lot of those books are quite old now so I'd expect you to have some opinions on what part is timeless wisdom and what part is out of date. You should also be looking to the books that are outside your direct area of responsibility, about design, user testing, management. Even if that's not your bread and butter, knowledge of those areas will be increasingly valuable to you.

I'd also expect you to have experience with and opinions on the use of AI in coding and in products.

With 7 years experience I would be looking to you to be guiding people on the team and and taking on projects and decisions.

Finally on much more practical note, we found at our size (15 person company with a dev team of 5) that we would basically never get job applications from adverts so half the time we wouldn't even put one up. You'd be wise to talk to some recruiters. It's also very much in their interest to get you hired so they can give you much more specific advice.