Can I take my iPhone 11 Pro Max in the shower or not? Will it be fine?

The IP water resistant rating is never a guarantee against damage from any water exposure. Water damage also voids the warranty. iPhones are not designed to be deliberately exposed to our used in water.

About splash, water, and dust resistance of iPhone 7 and later - Apple Support

No.

yes, at your own cost, don’t purposely put it in the water but if it does get damaged it’s on you apple doesn’t cover water damage