Not a vet, but I've started a few dozen or so fig plants from cuttings. What you see is very typical. I don't know what it is or why it happens but it appears to be quite normal and the plants continue to thrive in spite of it. As a matter of fact I'd guess that it is just the plant healing itself and closing off that opening. That's my two cents.

I live in central Florida, should I try to keep rain fro collecting in there or is that also of no concern? I felt like it was probably just a drying/ healing phase but I’d feel dumb to lose it to something that could be fixed

It is normal for the cut end of a cutting to die back. It will seal itself off. No need to worry about rotting.

Mikey,

That hole is perfectly normal, even though it looks worrisome. Fig wood is very soft, and the centers of stems are pithy. They tend to dry out and get hollow when cut and exposed to air, light, water... To the best of my knowledge fig wood is not used in wood working, furniture making, etc., for that very reason. It just is good to grow fruit upon!

As your healthy looking fig tree grows and the trunk thickens, the hole will just become less and less noticeable as tissue builds up until it is gone.

Moses