I designed a 25° GoPro mount for the AMAXinno Freestyle 5, 6 and 7
This mount works with a Session 5 and the TBS glass ND Filters (https://www.team-blacksheep.com/products/prod:ndfilter_nd8)
You just put the ND filter into the mount and then slide in the GoPro in.
If you don't use the ND filter, you can use the spacer instead, so you don't have to change the mount. (print it in PLA or similar)
The GoPro fits quite well, if you want you can use a 20mm LiPo strap around it to secure it even more (not required)