Website being directed to <domain>/blog for some reason

I set up apache2 server. The following is in /etc/apache2/sites-enabled/default-ssl.conf.

<IfModule mod_ssl.c>
        <VirtualHost _default_:443>
                ServerAdmin webmaster@localhost
                DocumentRoot /var/www/html
...

<br>
If I visit https://www.example.com/index.html it displays the content of /var/www/html/index.html file as expected. However, if I just visit https://www.example.com, it redirects to https://www.example.com/blog. I can't find anything in /etc/apache2 directory that contains "blog" at all.
<br>I did try to put a wordpress "blog" folder inside /var/www/html before and have a "blog" database in mysql. But I didn't really get it to work and tried to abandon it. Now it appears I am stuck with it and I can't figure out where it is enabled. I also noticed, if I visit http://www.example.com (not https) it doesn't redirect to /blog but displays index.html content.
<br>Appreciate if anyone can explain how/why apache2 decides to redirect https://www.example.com to https://www.example.com/blog. Thanks.

Login to your WordPress Dashboard, and go to Settings, then General. There will be two entries: WordPress Address and Site Address. It's likely that one or both entries will have "https://www.example.com/blog" as the value. Update these URLs and click on Save Changes at the bottom of the page.

However, if you cannot access the WordPress Dashboard, you'll have to review the database. Check your WordPress database, specifically the "wp_options" table; name varies by prefix, but "wp_" is default. In it, there are 2 entries which tell the WordPress site where it is hosted. Here is the MySQL query you can run to see what it says:

SELECT * FROM wp_options WHERE option_name IN ('home', 'siteurl');

You can update the fields with this query:

UPDATE wp_options SET option_value = 'https://www.example.com/' WHERE option_name IN ('home', 'siteurl') LIMIT 2;

The home (WordPress Address) vs siteurl (Site Address) entries differ in that the home entry is where your site can be reached, and siteurl is the URL of where the site content is located (DocumentRoot). Given your situation, it would appear that your home will have "/blog" and your siteurl will have the correct URL. Here is the WordPress documentation regarding the siteurl entry.

As for http vs https, that would depend on your sites-available configuration, but you can also force https with your .htaccess file, and both home and siteurl URL entries.

EDIT: as a quick fix, you can also update your wp-config.php file for the respective entries, but the better, permanent solution is to use the WordPress Dashboard (or manually updating the database for the same fields).