Instax SQ in 6x6 camera
I've been playing around recently shooting Instax wide in 4x5 using a polaroid holder and defunct single shot Polaroid sleeves to hold the film.
I just tried SQ in a 6x6 folder and though a bit fiddly and requiring a dark bag. Depending on the camera the film will fit across the gate so you load a sheet in the dark; take the shot then, in the dark, I unloaded the film and taped it to a old Quickload sleeve in an ancient 500 holder (very cheap to buy) and pulled through to process. Works well.
The light leak in the top corner is because I did not place the film pack in a dark box after I removed a sheet and replaced the dark slide.