@koa/router@15 now ships its own types, which are incompatible with @types/koa__router.

@types/koa__router@12.0.5:

declare namespace Router {
  // ...
}

export = Router;

@koa/router@15.0.0:

export { /* ... */ R as Router,  /* ... */  R as default } from './layer.mjs';

The code generated by the koa template does not work with the new types, so we should upgrade the import to import type { Router as KoaRouter} from '@koa/router'; - a breaking change that we can sneak in with v7