Reward points/gift card

You cannot buy Google Play gift cards with Microsoft Rewards Points as they aren't available on Microsoft Rewards or Microsoft gift cards. If you happen to have a redeemed Amazon gift card tied to your Amazon account, you may be able to just search Google
Play gift cards on Amazon and purchase it with your available Amazon credit. Using the Redeem tab on Microsoft Rewards, going to shop, and then selecting the Amazon gift card (if you have enough points) may be able to get you a Google Play gift card you are
looking for on Amazon. Please understand that may work, it is not guaranteed to work.

As another user had pointed out, you could also try and redeem your rewards points for a Walmart or Target eCard (online gift card similar to Amazon) and buy a Google Play gift card through their websites or online or in store. Those are also not guaranteed
to work but may work.

Google Play gift cards aren't currently an available reward option but there are plenty others.

Do activities in the Rewards program to earn Rewards points, then use those points to redeem Robux gift cards.

Always save your rewards points until you see something you really want. If I remember correctly, reward points are forever but redeemed gift cards through microsoft rewards count as promotional gift cards and you only have 90 days to use them.

If you have enough Microsoft reward points, then you need to redeem the reward points for Xbox/Microsoft Gift Cards on the redeem page of Microsoft rewards. Then once the gift card codes have been emailed to you, then you can redeem those gift card codes on https://account.microsoft.com/billing/redeem Once you have enough money from the Xbox Gift Cards, you can then purchase Minecraft from the Microsoft Store or Xbox Store (depending on which version you want).

What points are you trying to redeem? Rewards points or do you have a gift card?