As of my last knowledge update in September 2021, Threads by Instagram is a separate app designed for private messaging and close friends' communication. It is tightly integrated with Instagram, and blocking someone on Threads essentially blocks them from interacting with you on both Instagram and Threads. There isn't a way to block someone on Threads but not on Instagram within the app's functionality. However, you can control who can send you messages on Instagram itself without affecting Threads. To do this, you can use the "Message Requests" feature on Instagram to filter who can send you messages. Here's how: 1. **Open Instagram**: Open the Instagram app on your device. 2. **Go to Your Inbox**: Tap the paper airplane icon in the upper-right corner of the Instagram feed to access your inbox. 3. **Access Message Requests**: At the top of your inbox, you'll see the primary inbox with messages from your friends. Below the primary inbox, you'll see a section called "Message Requests." This is where messages from users who are not already your followers or friends are sorted. 4. **Review Message Requests**: In the Message Requests section, you can review messages from users who aren't following you. You can choose to accept or decline these message requests. 5. **Decline Message Requests**: If you receive a message request from someone you want to block on Instagram but not on Threads, you can decline the message request. This will prevent them from sending you messages in your primary inbox on Instagram. Please note that this method only applies to messages in your primary Instagram inbox. If you've already been communicating with someone through Threads, blocking them on Threads will affect your communication on both platforms. Instagram and Threads features may have evolved or changed since my last update in September 2021, so it's a good idea to check the most recent versions of both apps for any updates or changes to their blocking and messaging features.