Hi there, I am John J.D., a fellow Microsoft user like you.
I understand you're looking to get some Robux for free using Microsoft rewards. To get free Robux, you can use Microsoft Rewards. Here's how: https://www.microsoft.com/en-us/rewards/about
Once you've collected enough points, you can exchange them for Robux. Simply log into your Microsoft Rewards account https://rewards.bing.com/redeem/ and go to the Redeem tab. You can search for Robux and see if they're available.
Currently, the Robux reward is out of stock, and it's uncertain when Microsoft will restock it. Many users are eagerly waiting for it to become available again, so it's essential to keep an eye on the redemption page for any updates. Unfortunately, there hasn't been an official announcement regarding the availability of rewards. Stay tuned, and hopefully, they'll be back soon!
John J.D.