•Increase the text size of messages in Messages: In Messages, choose Messages > Preferences, click General, then move the “Text size” slider to the right. •Increase the text.

How To Make Text Bigger On Mac
You can set a single preferred size for text across multiple apps and on the desktop. On your Mac, choose Apple menu > System Settings, then click Accessibility in the sidebar. Click Display, scroll down to Text, then click “Text size.” Open Display settings for accessibility for me