The Session filters are just over 1mm thick (1mm for the glass, plus the adhesive), and fit into most mounts. If you have a mount that is designed to have the GoPro *Session* inserted from the side and it fits very tight, then it may not be possible to insert the camera with a filter attached. You can try putting the filter on after the camera is already in the mount if there is room. As a last resort, you can try cutting just enough of the TPU on the front away to make room to get the lens on.
The best mounts and protectors for the session are rear-entry. Anything like this one works really well and protects the filter.
The Hero filters will fit in any mount that does not have material up against the front of the lens.