esbuild implements TypeScript's legacy decorators when experimentalDecorators is set in tsconfig, and added support for the standard JavaScript decorators proposal in 0.21.0. What it does not implement, and states will not implement, is emitDecoratorMetadata.
That option makes TypeScript emit design:type, design:paramtypes, and design:returntype entries via Reflect.metadata, which requires full type information that a single-file transformer does not have. Frameworks that use it for dependency injection by constructor parameter type, notably NestJS and TypeORM, therefore break: injection resolves to undefined or throws about an unresolvable parameter, with no build error.
The options are to compile those files with tsc or SWC, which does implement the metadata emit, or to remove the dependency on it by annotating injection sites explicitly with @Inject(Token) and by giving ORM columns explicit types. This is the most common reason a NestJS project cannot simply swap its build to esbuild.