The website does not work properly after changing PHP

Same thing happened to me. I was setting up a brand new site on PHP 8.0, everything was working fine until I installed OceanWP theme. As soon as I did I got an error:

“There has been a critical error on this website. Please check your site admin email inbox for instructions.

Learn more about troubleshooting WordPress.”

Doesn’t work with 8.2, 8.1 or 8.0. As soon as I switch to 7.4 everything works fine.

I’ve tried other themes and they had no problem. I also don’t have any plugins activated. The only change from the base installation of WordPress has been OceanWP.

I switched to PHP 8.0 and the site immediatly breaks.
There are no active plugins.
OceanWP is the only change to the base WordPress installation. Not a child theme.
Doesn’t happen with any of the default themes.

[15-Nov-2023 19:29:37 UTC] PHP Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 2621440 bytes) in /home/urnplates/public_html/wp-admin/includes/template.php on line 1316

[15-Nov-2023 19:30:47 UTC] PHP Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 2621440 bytes) in /home/urnplates/public_html/wp-admin/includes/template.php on line 1270

[15-Nov-2023 19:30:49 UTC] PHP Fatal error: Allowed memory size of 41943040 bytes exhausted (tried to allocate 2621440 bytes) in /home/urnplates/public_html/wp-admin/includes/template.php on line 1270

The line at 1270 is:
$filename = preg_replace( ‘|^/([^/]/).$|’, ‘\1’, $filename );

The entire section of code is:

/**

• Internal helper function to find the plugin from a meta box callback.
  *
• @since 5.0.0
  *
• @access private
  *
• @param callable $callback The callback function to check.
• @return array|null The plugin that the callback belongs to, or null if it doesn’t belong to a plugin.
  */
  function _get_plugin_from_callback( $callback ) {
  try {
  if ( is_array( $callback ) ) {
  $reflection = new ReflectionMethod( $callback[0], $callback[1] );
  } elseif ( is_string( $callback ) && str_contains( $callback, ‘::’ ) ) {
  $reflection = new ReflectionMethod( $callback );
  } else {
  $reflection = new ReflectionFunction( $callback );
  }
  } catch ( ReflectionException $exception ) {
  // We could not properly reflect on the callable, so we abort here.
  return null;
  } // Don’t show an error if it’s an internal PHP function.
  if ( ! $reflection->isInternal() ) { // Only show errors if the meta box was registered by a plugin. $filename = wp_normalize_path( $reflection->getFileName() ); $plugin_dir = wp_normalize_path( WP_PLUGIN_DIR ); if ( str_starts_with( $filename, $plugin_dir ) ) { $filename = str_replace( $plugin_dir, '', $filename ); $filename = preg_replace( '|^/([^/]*/).*$|', '\\1', $filename );$plugins = get_plugins(); foreach ( $plugins as $name => $plugin ) { if ( str_starts_with( $name, $filename ) ) { return $plugin; } }} } return null;
  }