I have using all your code and try to create table and module...
1. Please add setup_version in module.xml file
<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Test_Module" setup_version="0.0.1">
        <sequence>
            <module name="Magento_Catalog"/>
        </sequence>
    </module>
</config>
 2. Please add these two line in your InstallSchema.php code..
$installer = $setup;
$installer->startSetup();
 
<?php
namespace Test\Module\Setup;
use Magento\Framework\Setup\InstallSchemaInterface;
use Magento\Framework\Setup\ModuleContextInterface;
use Magento\Framework\Setup\SchemaSetupInterface;
use Magento\Setup\Exception;
class InstallSchema implements InstallSchemaInterface
{
    public function install(SchemaSetupInterface $setup, ModuleContextInterface $context)
    {
        $installer = $setup;
        $installer->startSetup();
        try {
            $table = $setup->getConnection()
                ->newTable($setup->getTable('test_custom_table'))
                ->addColumn(
                    'test_id',
                    \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
                    null,
                    ['identity' => true, 'unsigned' => true, 'nullable' => false, 'primary' => true],
                    'Test ID'
                )
                ->addColumn(
                    'test_content',
                    \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
                    255,
                    ['nullable' => false, 'default' => ''],
                    'Test Content'
                )->setComment("Test Custom table");
            $setup->getConnection()->createTable($table);
        } catch(Exception $err) {
            \Magento\Framework\App\ObjectManager::getInstance()->get('Psr\Log\LoggerInterface')->info($err->getMessage());
        }
    }
}
 Once the extension is created, then we are creating installSchema.php file after executing the extension. Therefore, we have deleted the module form setup_module table and again run the command ....
php bin/magento setup:upgrade
php bin/magetno setup:static-content:deploy -f
php bin/magento cache:flush