I’ve always been full stack and feel like I’d be bored just focusing on one area. am I deluding myself?

I did this when I was young. Sometimes annoying little assholes just wanna feel powerful

I’m still waiting for webassembly to take off

I would say C# is a better bet as it abstracts a lot more from you than cpp. And as the name suggests the syntax is much like C so if you already have some basic understanding you should be fine. Also as others have said you’d is a learning opportunity, try to have fun with it!