Ich nieße viel.

English Translation

I sneeze a lot.

Warum ist hier “ß” statt “s”?

You’re right, “ß” is wrong here.
But it’s one of the mistakes that germans make. It’s probably a contamination by similar words that do have an “ß” there, such as “genießen” and “gießen”.

As @pitti42 says, the correct spelling is “niesen”.

Where does this mistake come from? There’s a rule to write “ß” instead of “s” whenever there are two vocals next to each other, such as “ie”. But “niesen” seems to be an exception (since there are also words like “genießen”) of which the author didn’t know.

I would additionally argue that “viel” is wrong here, and colloquial at best. You wouldn’t say “I sneeze much”, would you? I would prefer “Ich niese häufig” or “Ich niese oft”.

In my opinion both “viel” and “oft” work here, but have a slightly different meaning.

You claim that noone would say “I sneeze much”, but the english sentence uses “a lot” which is basically synonymous with “much”.

There are other examples where you can use “viel” instead of “oft”:
Ich reise viel. or: Ich bin viel auf Reisen.
Ich arbeite viel.
Ich lese viel.

And it’s especially apparent with “arbeiten” and “lesen”, that “oft” is not necessarily the same as “viel”. You can read a whole book in one session, but rarely have such a session. “oft” is only about frequency, while “viel” is kind of an accumulated amount over the number of occurrences, i.e. a combination of both.

So, with sneezing it can mean that it may not be that often, but when I do sneeze, it’s for 5 minutes straight.