There's a project that calls itself a "wifi repeater" at
It includes support for an ENC28J60 ethernet adapter connected via SPI.
It has some serious limitations.
First, it's really a NAT (Network Address Translation) router, not a Wifi extender, though it can effectively extend wifi. However, devices being extended will not be able to communicate with devices on the original network via broadcast or multicast. This will break some applications and many IoT devices.
Also, devices on the original network will not be able to originate connections to devices on the extended network.
But if you just have some devices that only need to talk to the Internet and are a little too far for your router, this should work for them.
Also, the ESP8266 can only get about 5Mbps through it (I'm actually surprised it's that high). You probably won't be able to reliably stream video - definitely not 4K video. It's not a good choice for connecting a television and probably won't work well with security cameras.
Finally, as @Juraj mentioned, it's not an Arduino project. You'll need to install the NON-OS SDK and toolchain to build it. It does include a pre-built image and instructions on how to flash it.
I haven't used it and can't promise that it will work well, but it's the closest thing I'm aware of to what you're looking for.