I cannot unlock all champions of League of Legends

You'll have to contact their support, as all of this is on their servers. Xbox is only serving as authentication

Hi,Ömer! I'm Luis, a fellow Xbox Gamer . Thanks for reaching us out here.

Ok If you’re an Xbox Game Pass member and your Riot Account isn’t receiving Game Pass member benefits more than 24 hours after linking your Xbox profile, you will need to contact Riot Player Support.

https://support.riotgames.com/hc/en-us?_gl=1

Note: This is a non-Microsoft website. The page appears to be providing accurate, safe information

I did but nothing was changed

Hi, I'm , an Independent advisor and I can surely help you.

Don't worry we will work on this together. Can you please try to sign out then sign in your account then check it again?

Thanks!

Thanks for your response, Nifrendiel. To confirm, this is one of the Microsoft Rewards offers, right?

If so, you could also reach out to the Microsoft Rewards team to check it on their end by sending them a ticket here https://go.microsoft.com/fwlink/p/?LinkID=823675