PHP Startup: Unable to load dynamic library 'wddx.so'

Nextcloud version _(20.0.1)
Operating system and version _(Ubuntu 18.04)
Apache or nginx ( Apache 2)
PHP version _( 7.4.12)

The issue you are facing:

Is this the first time you’ve seen this error? : YES after update the PHP from 7.2 to 7.4 with NC 20.0.1

Steps to replicate it:

when ever login NC with admin and moving to logging page

The output of your Nextcloud log in Admin > Logging:

PHP Startup: Unable to load dynamic library 'wddx.so' (tried: /usr/lib/php/20190902/wddx.so (/usr/lib/php/20190902/wddx.so: cannot open shared object file: No such file or directory), /usr/lib/php/20190902/wddx.so.so (/usr/lib/php/20190902/wddx.so.so: cannot open shared object file: No such file or directory)) at Unknown#0

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

<?php
$CONFIG = array (
  'memcache.local' => '\\OC\\Memcache\\APCu',
  'instanceid' => 'octyx37480li',
  'passwordsalt' => '8HkhNUr6y4CI2uvEzTVoKHePF5wMFL',
  'secret' => '1rmRYgJl6Ag66StkMetiR4nmZao5ENMlLmMmQtZXq2xq2MrK',
  'trusted_domains' =>
  array (
    0 => '192.168.1.55',
  ),
  'datadirectory' => '/data',
  'dbtype' => 'mysql',
  'version' => '20.0.1.1',
  'overwrite.cli.url' => 'https://192.168.1.55',
  'dbname' => 'admin',
  'dbhost' => 'localhost',
  'dbport' => '',
  'dbtableprefix' => 'oc_',
  'mysql.utf8mb4' => true,
  'dbuser' => 'admin',
  'dbpassword' => 'PASSWORD',
  'installed' => true,
  'ldapIgnoreNamingRules' => false,
  'ldapProviderFactory' => 'OCA\\User_LDAP\\LDAPProviderFactory',
);

The output of your Apache/nginx/system log in /var/log/____: apache error logs

PHP Warning:  PHP Startup: Unable to load dynamic library 'wddx.so' (tried: /usr/lib/php/20190902/wddx.so (/usr/lib/php/20190902/wddx.so: cannot open shared object fi$
[Sun Nov 01 06:25:01.847182 2020] [ssl:warn] [pid 7374] AH01906: 192.168.1.55:443:0 server certificate is a CA certificate (BasicConstraints: CA == TRUE !?)
[Sun Nov 01 06:25:01.847459 2020] [ssl:error] [pid 7374] AH02217: ssl_stapling_init_cert: can't retrieve issuer certificate! [subject: CN=192.168.1.55,O=LOCAL,L=Tr$
[Sun Nov 01 06:25:01.847474 2020] [ssl:error] [pid 7374] AH02604: Unable to configure certificate 192.168.1.55:443:0 for stapling
[Sun Nov 01 06:25:01.847572 2020] [mpm_prefork:notice] [pid 7374] AH00163: Apache/2.4.29 (Ubuntu) OpenSSL/1.1.1g configured -- resuming normal operations
[Sun Nov 01 06:25:01.847583 2020] [core:notice] [pid 7374] AH00094: Command line: '/usr/sbin/apache2'
[Sun Nov 01 09:54:58.510567 2020] [mpm_prefork:notice] [pid 7374] AH00169: caught SIGTERM, shutting down

had the same problem, flooding my logs, found out:

WDDX is part of PHP, but is deprecated and not part of PHP 7.4 anymore (see site in PHP manual).

I could solve the problem by switching back to PHP 7.3 in the webhosting configuration. If it’s your own server, you could try the link below.

credits: found this info via the guide Enable WDDX … in PHP 7.4

Thanks I will try it