Functional Comment Section using MERN stack

This is the first time I've used a few technologies in my own project such as React's context and useMemo, and styled components. Comments on any part of my project are appreciated, however I would mostly like to hear advice on my general React practices. I tried to apply a lot of what I've learned about React but I want to make sure I'm still using everything in the right places and correctly. I am also curious about what you think of my server-side code. What do you think about the general structure? While this is a small project, would you suggest any additions to security or validation?