ext_tables.php

$tmp_test_columns = array(

  'test' => array(
		'exclude' => 0,
		'label' => 'LLL:EXT:test/Resources/Private/Language/locallang_db.xlf:tx_test_domain_model_person.test',
		'config' => array(
			'type' => 'input',
			'size' => 30,
			'eval' => 'trim'
		),
	),
);

t3lib_extMgm::addTCAcolumns('fe_users',$tmp_test_columns);

$TCA['fe_users']['columns'][$TCA['fe_users']['ctrl']['type']]['config']['items'][] = array('LLL:EXT:test/Resources/Private/Language/locallang_db.xlf:fe_users.tx_extbase_type.Tx_Test_Person','Tx_Test_Person');

$TCA['fe_users']['types']['Tx_Test_Person']['showitem'] = $TCA['fe_users']['types']['Tx_Extbase_Domain_Model_FrontendUser']['showitem'];
$TCA['fe_users']['types']['Tx_Test_Person']['showitem'] .= ',--div--;LLL:EXT:test/Resources/Private/Language/locallang_db.xlf:tx_test_domain_model_person,';
$TCA['fe_users']['types']['Tx_Test_Person']['showitem'] .= 'test';

ext_tables.sql

#
# Table structure for table 'fe_users'
#
CREATE TABLE fe_users (
  tx_extbase_type varchar(255) DEFAULT '' NOT NULL,
);

#
# Table structure for table 'tx_test_company_person_mm'
#
CREATE TABLE tx_test_company_person_mm (
	uid_local int(11) unsigned DEFAULT '0' NOT NULL,
	uid_foreign int(11) unsigned DEFAULT '0' NOT NULL,
	sorting int(11) unsigned DEFAULT '0' NOT NULL,
	sorting_foreign int(11) unsigned DEFAULT '0' NOT NULL,

	KEY uid_local (uid_local),
	KEY uid_foreign (uid_foreign)
);

ext_typoscript_setup.txt

config.tx_extbase{
    persistence{
        classes{

            TYPO3\CMS\Extbase\Domain\Model\FrontendUser {
                subclasses {
                    Tx_Test_Person = Radmiraal\Test\Domain\Model\Person
  				
          		}
            }
            Radmiraal\Test\Domain\Model\Person {
                mapping {
                    tableName = fe_users
                    recordType = Tx_Test_Person
                }
            }
            
    	}
    }
}

ExtensionBuilderModelConfig

Domain model config:

Domain object settings > Extend existing model class: \TYPO3\CMS\Extbase\Domain\Model\FrontendUser