The “may affect Wi-Fi and Bluetooth connections” warning simply serves as a reminder that 2.4GHz WiFi Channels and Bluetooth occupy the same radio spectrum - and may cause mutual interference that potentially degrades performance of both.
Whilst 2.4GHz WiFi and Bluetooth devices often coexist without issue, problems can occur. Using 5GHz WiFi channels, in preference to 2.4GHz, completely avoids potential interference. As such, where you are able to do so, this approach is recommended.
As for issues with the Logitech K380 Keyboard, speaking only from personal experience, I have not noted any noticeable loss of performance attributable to RF inference between the iPad and keyboard.
Should you experience issues, these WiFi settings are recommended. If using 2.4GHz WiFi is unavoidable, you should avoid using “wide channels” (different Router manufacturers use various names for names to describe these options).