Have you installed any themes or plugins? Something may be preventing access to the dashboard.
Under Site administration ▸ Appearance ▸ Navigation what is Home page for users set to? If it's Dashboard try changing it to Site. If you can't log into the site to change it, try adding:
$CFG->defaulthomepage = 0;
to config.php (before the require_once(__DIR__ . '/lib/setup.php')).
server {
server_name poc-moodle.xxxx.com;
root /opt/moodle;
# Cloudflare
set_real_ip_from 173.245.48.0/20;
set_real_ip_from 103.21.244.0/22;
set_real_ip_from 103.22.200.0/22;
set_real_ip_from 103.31.4.0/22;
set_real_ip_from 141.101.64.0/18;
set_real_ip_from 108.162.192.0/18;
set_real_ip_from 190.93.240.0/20;
set_real_ip_from 188.114.96.0/20;
set_real_ip_from 197.234.240.0/22;
set_real_ip_from 198.41.128.0/17;
set_real_ip_from 162.158.0.0/15;
set_real_ip_from 104.16.0.0/12;
set_real_ip_from 172.64.0.0/13;
set_real_ip_from 131.0.72.0/22;
set_real_ip_from 2400:cb00::/32;
set_real_ip_from 2606:4700::/32;
set_real_ip_from 2803:f800::/32;
set_real_ip_from 2405:b500::/32;
set_real_ip_from 2405:8100::/32;
set_real_ip_from 2a06:98c0::/29;
set_real_ip_from 2c0f:f248::/32;
real_ip_header CF-Connecting-IP;
location / {
try_files $uri /index.php$is_args$args;
}
location ~ [^/]\.php(/|$) {
fastcgi_pass unix:/var/run/php/php7.4-fpm.sock;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_param PATH_INFO $fastcgi_path_info;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
include fastcgi_params;
fastcgi_param PATH_INFO $fastcgi_path_info;
fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
}
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/poc-moodle.xxxx.com/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/poc-moodle.xxxx.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
}