Apple sells and installs screen protectors in their stores all day, every day. You can't order an iPhone from Apple, with one preinstalled, but you can buy one from Apple as an accessory and install it yourself.
Now, to the "need." If you would be OK, with scratches appearing on your screen and they wouldn't bother you, then no, you don't need one. But if you want to keep your phone's screen pristine and scratch free, then yes, I can't recommend a screen protector enough.
Ceramic shield is great, but to me, an unfortunate name. It might give some a false sense of getting a phone whose screen can't be scratched. Glass is glass and no one has yet created a glass formula which can't be scratched. What Ceramic Shield does and does REALLY well, is make it harder for the glass to break in a fall. That's a tradeoff as glass which is less likely to break, is actually easier to scratch.
You don't have to buy your screen protector from Apple. You can buy one from literally thousands of manufacturers. My two favorites are from Spigen and a company I just learned about and have replaced the screen protector on my iPhone 16 Pro Max with one from Ragdo, which is perhaps the best screen protector I've ever used: https://www.amazon.com/dp/B0DFXZW6NX?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Since you are asking if you should have one, I'd hazard a guess you'd be upset if your screen got scratched? The singularly best way to ensure it won't is to put a screen protector on it, before you even turn it on.