WPMU using SUBDOMAIN site creation faliure

Greetings amazing devs!
I have a small problem revolving around Multisite subdomain site creation. I have read through quite some discussions regarding this but I seem to do something wrong. I have installed standard WordPress to my domain. After that, I have included the proper statement to my wp-config file and found the right .htaccess and wp-config settings in the backend of WordPress network setup. Now after that I have created a wildcard subdomain on my VPS server (running Apache) on latest PHP and MySql. I created the wildcard subdomain in the http_html directory as there is also my wp-config file (really just the whole WordPress). NOTE: I'm not getting any SSL insecure content in the backend and even on my sites that I created as standard WordPress! As that was a problem I had before this one.
The WPMU that I'm running already has LIKE A LOT of plugins installed and configured and it would suck if I had to redo everything. (using domain-mapping and pro-sites... the only 3rd-party are the theme ASTRA PRO and ELEMENTOR with pro addon)
My problem is that when I create a new site from my backend it is not created instead I get an https certificate error and description of the server folder structure ( index of: blah blah....) when I open the site from URL. If I open the site from backend it responds that it couldn't find the index.php file.
Now I am very confused as to what may be the problem. I know that the wildcard SSL is not set up correctly as it is not yet supported with AutoSSL. Next, I have some suspicion that I butchered some settings in my wp-config and .htaccess files.
Any help or insights would be really appreciated. If you need access to the WPMU I already granted access to it for 5 days starting today.
Best Regards :slight_smile: