So I was exploring my world in the new 1.17 generation, searching for Glow berries. I had searched through many minecart chests but hadn't found a single one, so I decided to make a creative mode copy of my world to try and help me find some.

I searched around through 5 or 6 Mineshafts and every chest I looked in contained no glow berries. To make sure I wasn't just having extremely bad luck, I created a new world with a blank seed to see if any Glow berries would spawn in a mineshaft there or not. I looked on 3 or 4 minecart chests and none had any glow berries in them. 

The Minecraft wiki says that there is a 38.7% chance for Glow berries to generate in a Minecart chest, but I haven't found any so far.