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Damn it, no way to login into my side. How do get into the WordPress Admin Backend?
Want to know the solution?
Here is how to fix it step by step:

STEP 1:
Enable debugging in wp-settings.php by adding these 3 lines

define( 'WP_DEBUG', true );

define( 'WP_DEBUG_DISPLAY', false );

define( 'WP_DEBUG_LOG', true );

STEP 2:
Check the logging file debug.log inside wp-content

STEP 3:
Clean up remove the debug instruction lines.
[31-Aug-2021 13:29:25 UTC] PHP Fatal error: require_once(): Failed opening required ‘/home/lalala/domains/xyz.com/public_html/wp-content/themes/Divi/et-pagebuilder/et-pagebuilder.php’ (include_path=’.:/opt/alt/php71/usr/share/pear’) in /home/ lalala /domains/ xyz .com/public_html/wp-content/themes/Divi/functions.php on line 7988

It looks like et-pagebuilder.php could not be found.

Indeed that files was not available inside the Divi/et-pagebuilder.

What I did is, to reupload the Divi theme.

Another thing I could probably do is to rename the theme folder: e.g. from Divi to Divi_backup as that would enable the default WordPress theme to load (if any, as recommended in the WordPress Site Health tool) at, I could access the wp-admin backend of the website.

TIP: It might be also handy to have some website monitoring in place. Only checking for “HTTP 200” would not solve anything in this case as the error page was a “valid” page.