You basically want: Ethernet only, Wi-Fi off.
Here’s the simple way + the “clean, permanent” way.


**1. Physically connect Ethernet**

1. Plug an Ethernet cable into the Pi’s RJ45 port.
2. Plug the other end into:

* Your router, or
* A network switch that’s connected to the router.

On [Raspberry Pi](https://www.ampheo.com/c/raspberry-pi/raspberry-pi-boards) OS (Desktop or Lite):

* By default, the Pi will try to get an IP via DHCP on Ethernet.
* You can check:
* Desktop: click the network icon → should see “eth0: Configured”.
* Terminal:

`ip addr show eth0`

Look for an address like 192.168.x.x under inet.

If Ethernet works, you’re online. Next step: kill Wi-Fi.

**2. Quick way: disable Wi-Fi from desktop (if you use GUI)**

On Raspberry Pi OS with GUI:

1. Click the network icon (top-right).
2. Find Wireless section.
3. Click Turn Off Wireless (or untick/disable Wi-Fi).

This will stop Wi-Fi until reboot / you turn it back on.
For a more permanent, system-level solution, use the next method.

**3. Permanent way: disable Wi-Fi via config (recommended)**
**Option A – Using raspi-config (easy, text menu)**

In a terminal:

`sudo raspi-config`

Then:

1. Go to System Options.
2. Choose S3 Wireless LAN or similar (depends on version).
3. There’s usually a menu to disable Wi-Fi (and Bluetooth).
4. Finish and reboot.

After reboot, the Wi-Fi interface (wlan0) should be gone or disabled.

**Option B – Disable Wi-Fi via /boot/config.txt**

This works on [Raspberry Pi](https://www.ampheoelec.de/c/raspberry-pi/raspberry-pi-boards) OS and is very clean:

1. Edit the config file:

`sudo nano /boot/config.txt`

2. Add this line at the end:

`dtoverlay=disable-wifi`

3. Save and exit (Ctrl+O, Enter, Ctrl+X), then reboot:

`sudo reboot`

After reboot:

Check interfaces:

`ip addr`

You should not see wlan0 anymore; only eth0 (and lo).

Tip: You can also disable Bluetooth similarly with
dtoverlay=disable-bt if you don’t need it.

**4. Optional: make sure Pi prefers Ethernet (metric)**

If you keep Wi-Fi enabled but want Ethernet preferred, set metrics via dhcpcd.conf:

`sudo nano /etc/dhcpcd.conf`

Add near the end:

interface eth0
  metric 100

interface wlan0
  metric 300

Lower metric = higher priority. Then restart networking:

`sudo systemctl restart dhcpcd`

But since you said disable Wi-Fi, the config.txt overlay is usually best.

**5. Quick summary**

* Connect Ethernet cable → router/switch.
* Verify eth0 has an IP (ip addr show eth0).
* Disable Wi-Fi:
* Easy: sudo raspi-config → disable wireless LAN → reboot.
* Clean: add dtoverlay=disable-wifi to /boot/config.txt → reboot.