It’s almost as if the PIC didn’t have hands on the controls once that turn started, or that was nil control response for whatever reason. Did something impact the windscreen? Did the seat slide back? Obviously serious structural/cable failure is another. Age is young, medical issues would be extremely unlikely.
Everything you have mentioned are "unlikely" events. While increased age brings increased chance of medical events there is never a stage in your life where a stroke/cardiac event, seizure, severe reaction to substance, blackout, etc etc could not happen. So unlikely as it may be, it is still possible at any age to be a factor and medical screening even for commercial pilots is not going to pick up most hidden things that might incapacitate you unless you have regular symptoms presenting prior.
I would consider a medical episode as likely as something hitting the windscreen. You could also say that structural failure of any kind is extremely unlikely given the conditions on the day, the aircraft is a common, reliable type, maintained to standards with regular inspections. Seat failure is extremely unlikely as the ADSB tracks don't show a pitch up to stall, unless they let go of the controls with the aircraft very out of trim, nose down. A stall is extremely unlikely because the speed seems too high, even with a significant pull up event, again which would show on the tracks. A spiral dive is extremely unlikely as the track does not indicate a turning spiral, and so on. Engine failure/fuel exhaustion is unlikely because they did not attempt to glide.
However just because something is very unlikely, does not mean it can not happen, especially when the event is an extremely unlikely event in itself. Also there is a lot of reliance on the track plots being accurate, at this point we have next to no idea what happened between turning downwind and it ending in a mess in the field, let alone come to any conclusions about what has happened.