TypoScript configuration of modules 

The backend module of an extension can be configured via TypoScript. The configuration is done in module.tx_<lowercaseextensionname>_<lowercasepluginname> or in module.tx_<lowercaseextensionname> . If the part _<lowercasepluginname> is omitted, then the setting is used for all backend modules of that extension.

Even in the backend the frontend TypoScript setup is used. The settings should be done globally and not changed on a per-page basis. Register them with \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::addTypoScriptSetup() in the extension's ext_localconf.php:

EXT:my_extension/ext_localconf.php 
use TYPO3\CMS\Core\Utility\ExtensionManagementUtility;

ExtensionManagementUtility::addTypoScriptSetup('
  module.tx_myextension.settings.itemsPerPage = 25
');
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Do not use ext_typoscript_setup.typoscript for this. It is not loaded on sites that use site sets, so a module showing a page of such a site does not see it. A module without a page tree only sees global TypoScript, see Breaking: #105728.

See the toplevel object "module" in the TypoScript reference for the available options.