Cannot verify server identity

Hello! I’ve recently got suspicious notification saying “the identity of ipo4.fun cannot be verified”. It appears out of the blue when I’m WhatsApp or so (not every time though)

I’ve downloaded couple of protecting apps since I am not really aware of these things to try to see if my phone got a virus or something like that but somehow it’s clean.

Are there any clues of what it can be and what can I do to fix this issue?

Thanks.