.htaccess crashes my wordpress website

Ok, I’ve struggled with this problem for several days now, and I don’t know how to fix it. Apparently I need to create an .htaccess file in order to allow my users to start accessing the posts and pages in my wordpress website, but adding an .htaccess in /var/www/seonbinovels.com/public_html just crashes the website. No error 500 or anything. Straight up crashes the website.

Here’s the code that I put into htaccess, seemed pretty ok to me…

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>

But the server just crashes. I’ve tried to see what was wrong by typing in apache2 -S in the console, but all I got was:

Apache error: Invalid Mutex directory in argument file:${APACHE_LOCK_DIR}

I don’t even know what that means… In any case, I checked that mod rewrite was indeed on, and I’ve also allowed overrides in 000-default.conf. And yet my site still crashes. Does anyone know how I can fix this…?

P.S. I’ve checked the apache2 error logs, and found hundreds of lines that said PHP warnings. I don’t know what that means or how I should fix it, but maybe that’s related to all this?