Hello, thank you for reaching out to Microsoft Q&A.
Yes, it is expected behavior that once you uncheck the Microsoft Rewards newsletter option in the Communication Preferences section, it disappears from that section completely. However, to subscribe to the Microsoft Rewards newsletter again, you will need to contact Microsoft Rewards Support directly, because the direct link to subscribe to the Rewards newsletter is no longer working:
https://aka.ms/rewardsnewsletter
To get in touch with Microsoft Rewards Support, go to https://rewards.bing.com/support and fill in all the details correctly. In the “Please select one category from the list below” section, choose “Subscribe or unsubscribe to newsletter”, and then click Submit.