How do I get rid of this annoying display from my Huawei P40 Pro?

If my Vodafone WLAN says goodbye in between and my cell phone switches to mobile data, I get the following message.

How do I deactivate the message permanently. I have enough mobile data and that's why it sucks for me what volume my cell phone draws 😁

Try deactivating "data saving" (you find this normally if you stay on the mobile data symbol for a long time)