Yes, lions have belly buttons. However, they are not like human belly buttons. Here is a screenshot from a video (I added the arrow and words).
All placental mammals have belly buttons. There are almost 400 species which give birth to live young who have been nourished before birth in their mother’s uterus via the placenta. The lion is one of these species as are all cats.
In the illustration on this page it is hard to see in detail the lion’s belly button partly because it is covered with fur and secondly because it is a screenshot from a video. It seems that whereas the human belly button is very noticeable, it is more discrete on lions. This may be because, as I understand it, lionesses (just like domestic cats) eat the placenta and umbilical cord immediately after birth. This may result in a neater repair job than is the case with humans.
This video may well disappear in time. Sorry but I have not control over its longevity.