>>> What team other then Texan Longhorn accept an invitation to the SEC in July 2021? 

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Based on the provided context, the only other team from the Big 12 that could accept an invitation to join the SEC, other than Texas, would be Oklahoma. This is because the text specifies that Oklahoma accepted an invitation to join the SEC alongside Texas, and no other team from the Big 12 is mentioned as having done so. Therefore, the answer is Oklahoma.