Since the release of PHP 8.5, the SoapClient::__doRequest() function has been updated with a new parameter (uriParserClass). So the declaration in AdsSoapClient.php is now incorrect, and you get this error:
Fatal error: Declaration of Google\AdsApi\Common\AdsSoapClient::__doRequest($request, $location, $action, $version, $one_way = 0) must be compatible with SoapClient::__doRequest(string $request, string $location, string $action, int $version, bool $oneWay = false, ?string $uriParserClass = null): ?string ...
For now, you must remain on 8.4.