My Philodendrom Xanadu is brown and dying?

Usually too dry or too wet.

Could it be getting sunburned? See if this helps?

https://www.houseplant411.com/houseplant/philodendron-xanadu-how-to-grow-care-tips

Have you thought about buying a moisture meter? That will let you know if it needs to be water of not. And the nice thing is that you can insert the wand and take the moisture reading at the plants root level.

They do not like a lot of water. Let them get dry then water. Brown leaves usually means to much water,

Rllambert is correct. Too little water turns leaves yellow, too much turns them brown. Place the pot in a saucer and water from the bottom up.

FIND THE ' PH ' OF THE NEW SOIL AND MAKE CORRECTION IF REQUIRED.. INTERNET SUGGESTS A SOMEWHAT ACIDIC READING BETWEEN 4.5 AND 6.0.

Hi from Sydney, Australia. As the other comments I would say that you have been watering too much. Is the soil soggy? If so you may need to purchase new potting mix. Just make sure the plant isn't sitting in water - just raise off the ground with, say, bricks or something else just so it doesn't get mushy. Or like the other comment, sit in a saucer and water from the base. Good Luck. (ps don't plant in the ground - they go 'feral' and are extremely hard to control. You can cut back, but they will grow again. Very vigorous. And can take over).