In the design tab, we have an option to increase the font size of the answers. It will help you increase the size of input that the respondents are providing. However, this size will apply to all the question"s answers. So if you wish to have a different size for the answer options of closed-ended questions than the text input, then for open-ended questions you need to use the design tab, and for other questions, you need to set the size for each answer option using the rich content editor.

Screenshot: https://prnt.sc/ajs4we5GclSQ

Rich content editor: https://www.questionpro.com/help/rich-content-editor.html