Are you trying to verify your domain (hosted by a third-party vendor) in Microsoft 365 admin center?
If you would like to update TXT records, you may need to perform this action in your domain provider's domain control panel.
Take Godaddy for example: Add a TXT record
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)
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