I can’t speak to the specifics of transferring from Java to C#, but as someone who recently had to re-learn/catch up on it and Dotnet for a job transition I can say what helped me after not touching it for nearly a decade.

I found a few people on YouTube that did project walkthroughs, and I followed along with them and built out their examples. I used C# 10 In A Nutshell as a reference when I felt I needed to dig deep on the various things the videos touched on or that I knew I’d be needing for the code base I was inheriting. I was preferential to Tim Corey, mostly because a lot of his videos felt up-to-date with the latest technologies and were easy to follow. He also has courses designed to be a boot camp for getting up to speed, I believe, on his website if that is an option for you.