It is not a scam. they are offering free Peacock to Xfinity rewards customers and Gigabit Internet customers. I received that email too and it did not work
I had the exact same issue. Here's what I did to finally get it to work.
1) log in to Xfinity and go to the Rewards page.
2) Find the Peacock offer "tile" and click it. It will say to wait 10 minutes or so
3) wait 20 min because Xfinity is slow
4) Close browser. Reopen. (or open a private window) Go back to Xfinity and click chat.
5) Log in to chat and then you should see a banner that will say "activate now" for peacock
6) Log in to that using either a new login or your pre-existing one
7) DONE
I had various issues along the way that made these steps the best for me. the banner wouldn't show in chat, primarily and then when I finally found and accepted the offer tile, I ultimately had to use a private window to get around some weird sign-in issues that wouldn't prompt the banner to appear.
I asked their support team for help prior to all this and they were - predictably - absolutely useless and had no understanding of what the issue was. They kept telling me to just sign up at Peacock's website and accept the $5.99 offer or sending me support links on how to download the Peacock app.