make sure you've reformatted the card to fat32.
Most modern sdcards come preformatted with ex-fat.
A lot of systems can't see exfat.

Sandisk are the best you can get - so check the formatting.
And creality do use dirt cheap electronics, so you might need a smaller card as well
https://www.amazon.com/SanDisk%C2%AE...6095303&sr=8-3

And i apologise in advance but this did made me laugh :
I am trying to get a Creality CR-10 Max to work for a friend. I know very little about 3D printers.
But presumably you know more than your friend :-)
And had the sense to ask :-)