Hello everyone. :)
I'm a little puzzled right now. I've tried to setup a Virtual host for my subdomain "forum.mywebsite.com". Because I need it for community software, as WordPress is already served by my main domain "mywebsite.com".

So I've followed this tutorial : https://linuxize.com/post/how-to-set-up-apache-virtual-hosts-on-ubuntu-18-04/

Required folder is created in var/www, with the same name as the subdomain. (forum.mywebsite.com)

When needed, I've created a new conf file in etc/apache2/sites-available :

code<VirtualHost *:80>
ServerAdmin mywebsite@gmx.fr
ServerName forum.mywebsite.com
ServerAlias www.forum.mywebsite.com
DocumentRoot /var/www/forum.mywebsite.com
<Directory "/var/www/forum.mywebsite.com">
AllowOverride All
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
</VirtualHost>

I think the setup is correctly done, but when I try to access the Public folder of my forum CMS with my browser, (forum.mywebsite.com/public), I got a redirection on my main WordPress page. The same when I just try to reach the root of my subdomain.

Apache2 rebooted and Virtual host enabled with a2ensite prompt.

DNS A record for subdomain is registered. (And actually works fine.)

Droplet was created with a Wordpress image already preinstalled.

So I wonder where is the potential issue ? Thanks ! :)