The Magento 2 default format of the URL, “sitename.com/admin” is vulnerable to bots. So, it is recommended to change admin URL in Magento 2.
Methods to Change Admin URL in Magento 2:-
Via SSH
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Manually
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Via Admin Panel
Read all three methods in detail at https://meetanshi.com/blog/change-admin-url-in-magento-2/