How to ensure www.example.com is redirected to example.com by using Nginx, Gunicorn and Let's Encrypt certificates ?

I’m using Gunicorn and Nginx on Ubuntu. I also installed Let’s Encrypt certificates for my example.com and www.example.com with option 2-Redirect to redirect all HTTP to HTTPS. Now I have the issue that the redirection from www.example.com to example.com is not working properly - it seems to me this happens after I installed Let’s Encrypt certificates (but I’m not exactly sure). When entering to browser, http://www.example.com/ is redirecting to https://www.example.com/ https://www.example.com/ stays https://www.example.com/

Here is the Nginx configuration:

server {
    server_name example.com www.example.com;

    location / {
        include proxy_params;
        proxy_pass http://unix:/run/exampleproject.sock;
    }

    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
    if ($host = www.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    if ($host = example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

    server_name example.com www.example.com;
    listen 80;
    return 404; # managed by Certbot
}

I’m really not Nginx expert so could you please suggest what to do - how to redirect all www.example.com to example.com and at the same time keep the functionality that HTTP is redirected to HTTPS ?

IMO, probably this part managed by Certbot is doing wrong - it’s just rewriting the whole $host part when redirecting instead of leaving out www:

    if ($host = www.example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot

Because this part is related to Gunicorn and I don’t see what could I do here but also I’m very far away of being Gunicorn expert to judge that :-)

    location / {
        include proxy_params;
        proxy_pass http://unix:/run/exampleproject.sock;
    }

Thank you !