Start by creating your form and choose Long Answer Text as the type of form field. Then click on the 3 dots in the lower right corner of your form field and choose Response Validation.
You have a couple of options, but you'll want to choose Length and then Maximum Character Count. Type in the number of characters that you want as your limit. If you'd like, you can also customize the error message that users will see. The default is a brief message saying that there is a maximum character limit of xxx.
