This is from an official core book of 5e dnd and the same description we have in baldurs gate 3.
You touch a willing creature. Until the spell ends, the target's skin has a rough, bark-like Appearance, and the target's AC can't be less than 16, regardless of what kind of armor it is wearing.
The important part it cannot be less than 16 that mean it can be more there is no description that forbid dexterity or shield.
I am playing dnd more than 25 years i know how much ts supposed to work.
The WoTC Sage Advice ruling confirming Barkskin doesn’t stack with other bonuses can be found on page 13 of the compendium at:
https://media.wizards.com/2016/downloads/DND/SA-Compendium.pdf
