Ghasts are invisible! They send out fireballs but you cannot kill or hit them because they are completely invisible.

To reproduce, go to the nether and wait for a ghast to "appear" (you will hear the noises but not see a ghast) and fireballs will be fired towards you

Video attached to show the scariest thing I have ever encountered in Minecraft!

I also notice the last time this was logged was 2016 and it was resolved so please don't resolve this one as it's a new issue and I've seen some other people comment that they have the same issue either invisible ghast or invisible fireballs