Please follow below tips to troubleshoot the issue:
1.Make sure the newly created domain is completely setup and healthy.
2.This feature is currently available to organizations that have no more than 10,000 total SharePoint sites and OneDrive accounts combined. Additionally, tenant renaming capability is not available for GCC, GCC High, and DoD.
3.According to this Microsoft article, please retry the renaming action after some time passes.
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