app.controller.ts

import { Controller, Get, Res, Next, Req } from '@nestjs/common';
import { join } from 'path';
import { Response, NextFunction, Request } from 'express';

@Controller()
export class AppController {
  @Get('*')
  get(
    @Res() res: Response,
    @Next() next: NextFunction,
    @Req() req: Request,
  ) {
    // here you can check if the requested path is your api endpoint, if that's the case then we have to return next()
    if (req.path.includes('graphql')) {
      return next();
    }
    
    // change the path to the correct html page path in your project
    res.sendFile(join(process.cwd(), '../client/dist/index.html'));
  }
}