Remixed from the Ender 3 Tool Holder - Gridfinity model by healthier on Thangs. I removed the rounded USB card reader slot that is needed for the microSD card reader that comes with the Ender 3 variants. I extended the block upwards and then recessed a rectangle that is a bit bigger than the CR-10 V3's USB card reader and a little over ⅓ of its depth. There is a bit of play so that it's easy to insert and remove and it sticks up over the base rim farther than the original so that it's easy to grab.

I paired this with a pair of https://www.printables.com/model/262541-printer-mounted-gridfinity-baseplate-v-slotbear so that it mounts on the left side under the Z brace. It makes it easy to remove but keeps it out of the way when I'm printing.