I am glad that your issue is resolved and thanks for sharing the update here.
By the way, since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others.", and according to the scenario introduced here: Answering your own questions on Microsoft Q&A, I would make a brief summary of this thread:
Issue Symptom:
When installing Office Standard 2021 from local source (Download the Office installation file on local machine in advance), the error message prompts up: "This product cannot be installed on the selected update channel."
Cause & Solution:
There is a problem with the installation file. Running the latest ODT with correct .xml file to download the correct installation package can solve this issue.
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