Fixed stl and blend files for original design https://www.thingiverse.com/thing:4071013. (Not my design)

There are 3D print files for GoPro 5-6-7 but I think 7 is better to use for portrait orientation.

For phones (likely IPhone) you can use https://www.aliexpress.us/item/2251832753194520.html to fix phone to grip.

For adjustable back and top straps use a face shield as donor.

Use eva foam for inner cover.