Используйте JS и browser.execute_script
Подсмотреть функцию для вставки можно в Selenide
browser.execute_script(s"return (function(webelement, text) {" +
"if (webelement.getAttribute('readonly') != undefined) return 'Cannot change value of readonly element';" +
"if (webelement.getAttribute('disabled') != undefined) return 'Cannot change value of disabled element';" +
"webelement.focus();" +
"var maxlength = webelement.getAttribute('maxlength') == null ? -1 : parseInt(webelement.getAttribute('maxlength'));" +
"webelement.value = " +
"maxlength == -1 ? text " +
": text.length <= maxlength ? text " +
": text.substring(0, maxlength);" +
"return null;" +
"})(arguments[0], arguments[1]);", element, text)
