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.

To disable core modules you can run these commands:

bin/magento module:disable Magento_LoginAsCustomer
bin/magento module:disable Magento_LoginAsCustomerAdminUi
bin/magento module:disable Magento_LoginAsCustomerApi
bin/magento module:disable Magento_LoginAsCustomerAssistance
bin/magento module:disable Magento_LoginAsCustomerFrontendUi
bin/magento module:disable Magento_LoginAsCustomerLog
bin/magento module:disable Magento_LoginAsCustomerPageCache
bin/magento module:disable Magento_LoginAsCustomerQuote
bin/magento module:disable Magento_LoginAsCustomerSales