As you may know Magento 2 Login as Customer extension by Magefan was integrated into the Magento 2.4.0 core, and we transferred the copyright for "Login as Customer" extension to Adobe. More about it you can read here.
So if you use Magento 2.4.x or greater you have 2 options:
1. Remove Magefan Login as Customer extension and use core Magento Login As Customer
2. Disable core Login As Customer and continue using original Magefan Login as Customer.