Can You Use a WiFi Extender as a Router?

Some extenders act as an access point when connected by Ethernet to an existing network. They may not provide routing or modem functions, so check the mode list.

A standard extender needs a network to repeat. Access Point mode also needs a wired upstream network; the extender does not create internet access alone.

Repeater mode relays a router's WiFi wirelessly. Access Point mode typically uses Ethernet to provide WiFi from a wired network.

It depends whether the modem also provides routing and a local network. Check both manuals; the extender alone may not supply the network functions required.