No, currently it is not possible to adjust the length of the dynamic comment box, as it is typically designed to collect open-ended inputs. However, as a workaround, you can use a Comment Box question type as a follow-up question and adjust its length through the question settings.
Screenshot: https://prnt.sc/A_Oe_XjT_PnN
Help File: https://www.questionpro.com/help/text-input-size.html
Can I add Character Limit to the dynamic comment box used in my survey?
Is data being collected from dynamic texts and comment boxes?