Problem with phpMyAdmin and PHP 7.2: “Warning in ./libraries/sql.lib.php#613 count(): Parameter must be an array or an object that implements Countable”

It’s possible that when you installed phpMyAdmin, the version in the repository (phpMyAdmin v4.6.6) was not fully compatible with PHP 7.2. There is a newer version available on the official website (v4.8 as of writing), which fixes these compatibility issues with PHP 7.2.

This error is caused by a line of code in /usr/share/phpmyadmin/libraries/sql.lib.php.
If you don’t want to wait for the repositories to update with the latest version, it is strongly recommended that you manually upgrade to the latest version of phpMyAdmin yourself.
Alternatively, you can make a change to sql.lib.php to temporarily fix the error.
Firstly, backup sql.lib.php before editing.
sudo cp /usr/share/phpmyadmin/libraries/sql.lib.php /usr/share/phpmyadmin/libraries/sql.lib.php.bak
Edit sql.lib.php in nano.
sudo nano /usr/share/phpmyadmin/libraries/sql.lib.php
Press CTRL + W and search for (count($analyzed_sql_results['select_expr'] == 1)
Replace it with ((count($analyzed_sql_results['select_expr']) == 1)
Save file and exit. (Press CTRL + X, press Y and then press ENTER)
Import/Export issues
If you are also getting an error Warning in ./libraries/plugin_interface.lib.php#551 under import and export tabs:
Backup plugin_interface.lib.php
sudo cp /usr/share/phpmyadmin/libraries/plugin_interface.lib.php /usr/share/phpmyadmin/libraries/plugin_interface.lib.php.bak
Edit plugin_interface.lib.php
sudo nano /usr/share/phpmyadmin/libraries/plugin_interface.lib.php
Press CTRL + W and search for if (! is_null($options) && count($options) > 0) {
If not found, try search for if ($options != null && count($options) > 0)
Replace with if (! is_null($options) && count((array)$options) > 0) {
Save file and exit. (Press CTRL + X, press Y and then press ENTER)