@PaoAX10 Hello,
If you want to block certain device connected to Range extender, please set up Access Control (Blacklist)on the range extender for that device
https://www.tp-link.com/support/faq/1268/
Due to Proxy Mode, Range Extender will replace each of its clients’ MAC address with a virtual MAC address generated automatically by Range Extender. Thus the router will take the virtual MAC address of the clients as their real MAC address. That is the reason why the MAC address in the router's management interface is different from the device's real MAC address. And if you want to set up Parental Control for devices , please enter the virtual MAC address of the clients. You could check this FAQ for more details: https://www.tp-link.com/support/faq/2019/