iPhone XR won't stop connecting to LTE when home wifi available

Hello superiormario.

Thank you for using Apple Support Communities. You might want to check and confirm that your device isn't using Wi-Fi Assist. This feature can automatically switch from your Wi-Fi to your cellular network: About Wi-Fi Assist - Apple Support

Turn Wi-Fi Assist on or off:

Wi-Fi Assist is on by default. If you don't want your iOS device to stay connected to the Internet when you have a poor Wi-Fi connection, you can disable Wi-Fi Assist. Go to Settings > Cellular or Settings > Mobile Data. Then scroll down and tap the slider for Wi-Fi Assist.

If this feature is already off, you might want to try additional troubleshooting steps. Try restarting your device first: Restart your iPhone - Apple Support

1.) Press and hold either volume button and the side button until the power-off slider appears.

2.) Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.

3.) To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

You might also need to reset your Network Settings:

On iOS15, tap Settings > General > Transfer or Reset iPhone > Reset > Reset Network Settings. This also resets Wi-Fi networks and passwords, cellular settings, and VPN and APN settings that you’ve used before. If you're using iCloud Keychain, these settings are also removed from other signed-in devices.

Also, if you have any pending updates available, it would be a good idea to install them. This can help resolve various issues. Just incase, this resource can guide you through the update process: Update your iPhone, iPad, or iPod touch - Apple Support

1.) Back up your device using iCloud or your computer.

2.) Plug your device into power and connect to the internet with Wi-Fi.

3.) Go to Settings > General, then tap Software Update.

4.) If you see two software update options available, choose the one that you want to install.

5.) Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.

We hope this information is helpful. Cheers.