How can I best implement the admin role in a Nest.js + React application?

I am writing a term project on the topic of a forum and want to separate the functionality for a regular user and an admin. My problem is that I don't know how to display a specific tab or link for accessing admin features after authorization, such as adding topics and so on..

I tried implementing role-based access control in my Nest.js + React application. I expected to be able to display a specific tab or link for accessing admin features after a user has been authenticated. However, I'm unsure of the best way to accomplish this within the application

There are many ways to skin this cat. I think we would require more information around how you tried implementing role-based access control in your nest.js application to give a more verbose answer.

What are you sending to your react application from nest.js when a user has been authorised?

If you are currently using Nest.js guards for authorization and RBAC, you could

import { ExtractJwt, Strategy } from 'passport-jwt';
import { PassportStrategy } from '@nestjs/passport';
import { Injectable } from '@nestjs/common';

@Injectable()
export class JwtStrategy extends PassportStrategy(Strategy) {
  constructor() {
    super({
      jwtFromRequest: ExtractJwt.fromAuthHeaderAsBearerToken(),
      ignoreExpiration: false,
      secretOrKey: 'secrete',
    });
  }

  async validate(payload) {
    return {
      userId: payload.id,
      userName: payload.userName,
      role: payload.role,
    };
  }
}

which can then be imported into your app.module file

import { JwtModule } from '@nestjs/jwt';
import { JwtStrategy } from './auth/jwt.strategy';

@Module({
  imports: [
    ...,
    JwtModule.register({ secret: 'secrete', signOptions: { expiresIn: '1h' } }),
  ],
  ...,
  providers: [..., JwtStrategy],
})
export class AppModule {}

Now you will have access to the role context in your frontend application.

Again this is just one of many ways to do this & I think without further information of what has been currently done, it would be hard to guide you in the right direction.