How to define a RegularExpresion Validation for an Controller Action Param, in TYPO3 v10/v11?

I’m updating an extension for usage in TYPO3 v10 or higher and have an issue with a regular Expression validator, i don’t know how to get in runnable in v10 or higher now. Tried the following:

/**
 * action list
 *
 * @param string $filterChar
 * @ExtbaseValidate("RegularExpression",options={ "regularExpression": "/^[0-9A-Za-z]{0,1}$/i" })
 * @return void
 */
public function listAction(string $filterChar = '') {

But i got the following exception:

Invalid validate annotation in ABCMyExtControllerMyController->listAction(): The following validators have been defined for missing param "$": RegularExpression

What i’m doing wrong and how can i fix it, or what is the correct definition now for a RegularExpression validator for an action parameter?