You could respond with a thoughtful comment that acknowledges their feelings and adds to the conversation. Here’s a suggestion:
"That's a great point! I really enjoyed the discussions as well. It's fascinating how sharing our different perspectives can enrich our understanding of the topics. I felt like I learned so much from everyone’s unique viewpoints. It’s nice to see how even in an online setting, we can create connections and engage with one another. What was your favorite discussion topic this semester?"
This way, you commend their thoughts while also encouraging further discussion.