I've been using c# since .net 2 which came out around the turn of the century (lol)
I'd happily call myself an expert. I can do anything I need to and easily dive into the standard library source code or even IL when needed.
But even then there are topics I could easily learn more on particularly the very performance focused struct features and intrinsics.
I've found LLMs to be super useful when you have a very specific question about a feature. I use bing ai at work so it sources all its answers and you can dive into the articles for more detail.
Programming is a never ending learning journey and you just have to keep going. When you get something you don't fully understand to a deep dive there are always resources for everything.
100% un-nesting that if would have been fine.