can you use "if ever there was" literally?

It's meant to be taken and interpreted literally. The "typical example" definition is just a further explanation. For example, "This was a perfect summer day if ever there was one" should be understood as "If a perfect summer day existed, this would be it".

Yes. "If there ever existed something like that, this would be it” is a pretty common usage. I hear it used like that more than the idiom in fact. (Central Texas, US English)

Can you explain why you think the regular usage isn’t literal?

Yes you can! Like if there were a Guinness world record for best post on a subreddit, this would be a candidate!

The idiom comes from the regular usage of the phrase. You can say things like "If ever there was a perfect pizza, this would be it." It's the same as saying "if there ever was," but its use as an idiom has cemented a slightly older word order. If you do it with other verbs it might sound a bit poetic or dated, like "If ever I go to that store, I'll get you one." It's not wrong, and it is used that way, but not commonly. That said, there are plenty of songs that use "if ever", such as "If Ever I'm In Your Arms Again."

You can absolutely be used literally. And often is. If ever there was a time to use that phrase literally, it would be here and now.