Hi Marek,
Go the same issue after upgrading to WP 5.4.1 last night.
Any advise on how we can solve it? I tried to downgrade WP with no success.
WordPress version 5.4.1
Current theme: Divi (version 4.4.6)
Current plugin: Image and video gallery from Google Drive (version 2.7.8)
PHP version 7.0.33
Error Details
=============
An error of type E_ERROR was caused in line 203 of the file /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/symfony/polyfill-intl-idn/Idn.php. Error message: Uncaught Error: Call to undefined function Sgdg\Vendor\Symfony\Polyfill\Intl\Idn\mb_ord() in /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/symfony/polyfill-intl-idn/Idn.php:203
Stack trace:
#0 /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/symfony/polyfill-intl-idn/Idn.php(130): Sgdg\Vendor\Symfony\Polyfill\Intl\Idn\Idn::listCodePoints('oauth2')
#1 /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/symfony/polyfill-intl-idn/Idn.php(80): Sgdg\Vendor\Symfony\Polyfill\Intl\Idn\Idn::encodePart('oauth2')
#2 /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/symfony/polyfill-intl-idn/bootstrap.php(55): Sgdg\Vendor\Symfony\Polyfill\Intl\Idn\Idn::idn_to_ascii('oauth2.googleap...', 0, 1, NULL)
#3 /home/dlaserne/public_html/wp-content/plugins/skaut-google-drive-gallery/bundled/vendor/guzzlehttp/guzzle/src/Utils.php(36): idn_to_ascii('oauth2.googleap...', 0, 1, NULL