I can only guarantee that a GoPro 7 fits, but it looks like the 5 and 6 share the same external design.
The gridfinity units are 2x2x8. Let me know if you need a shallower one (in height) and I'll help you out with that.
So many other GoPro holder designs don't include room for the camera's own case and that made them all deal beakers for me. That's what motivated me to design this one.
If you're happy with my work, consider buying me a coffee for just $1. Small gestures give more motivation than you might think. https://www.buymeacoffee.com/FastLaneEngineer