As much as I think C# at a platform level is a better tool for building backends, you'll get the better bang for the buck learning TypeScript if you don't already know TypeScript.
Then if you have the chance, you'll find C# an easy transition from TypeScript, IME. Learning C# first, on the other hand, will make you a better TS developer, in my opinion, because it will shape your approach to be more diligent about using types. This is something most JS/TS devs do very poorly and at scale, it's very hard to reason about code when it requires digging down several layers to find the actual types/shapes.
"Enterprise" frameworks like Nest.js are much more similar to ASP.NET or Spring Boot than they are to Express, Hono, or Elysia so once having experience with .NET Web APIs (or Spring Boot) will make Nest.js (for example) easier to pick up.
Then if you have the chance, you'll find C# an easy transition from TypeScript, IME. Learning C# first, on the other hand, will make you a better TS developer, in my opinion, because it will shape your approach to be more diligent about using types. This is something most JS/TS devs do very poorly and at scale, it's very hard to reason about code when it requires digging down several layers to find the actual types/shapes.
"Enterprise" frameworks like Nest.js are much more similar to ASP.NET or Spring Boot than they are to Express, Hono, or Elysia so once having experience with .NET Web APIs (or Spring Boot) will make Nest.js (for example) easier to pick up.