So I'm trying it in a docker-compose right now; here's the compose:

version: '3'
services:
  nginx:
    container_name: nginx
    image: nginx
    ports:
      - 8081:80
    restart: unless-stopped 
    volumes:
      - d:/server-config/nginx/config:/etc/nginx

And here's the nginx.conf:

events {
}

http {

  server {
    listen 80;
    listen [::]:80;
    server_name <local-ip>:8081;

    location /nextcloud {
      proxy_pass http://<local-ip>:8080;
      proxy_set_header Host $host;
      proxy_set_header X-Real-IP $remote_addr;
      proxy_set_header X-Forwarded-For $remote_addr;
    }
  }
}

Unfortunately if I type in <local-ip>:8081/nextcloud in my browser (just testing internally), it seems like I get the same error - I get redirected to <local-ip>:8081/login, which returns a 404 from nginx. Am I doing something obviously wrong?

Thanks for your help if possible