Could a cat be allergic to something out of the blue?

I've always switched litters , usually between fresh steps and scoop away.
Sometimes the scented, sometimes not.
NEVER had an issue.
I got the fresh step new one, which Im not even sure which one it is, it does smell similar to scoop aways.
But my cat has been sneezing non stop for 3 days.
None of my cats go outdoors, nothing new came inside.
All of them are healthy, and no other symptoms other then the sneezing

If you got something new, it's quite possible there is something in it that acts as an irritant for your kitty.
The same thing happened to us once when I got an unscented litter that was new to us. And it took our cat two or three days to completely stop sneezing after that litter was no longer even in the house.
Could you possibly do a test by switching back to a litter that has never caused any problems in the past? It wouldn't take long to find out if the new litter was indeed causing the sneezing.

YES allergies can come out of the blue ...

We just got rid of one that was causing Carly all sorts of problems. I noticed that I coughed horribly when cleaning out the box because of the perfumey dust. And then Carly's eyes started squinting and became really watery. Her ears seemed itchy also. We dumped it all and got an unscented one that we had used before. Within a day, Carly was much better.