Just looking for some ideas.............
The oil I drain out of my KTM 200 gearbox looks like this after a few hundred km.
Should it look like that ?
Drop a magnet in the oil and gently move it around, see if you get anything.
But being KTM it should have a sump Plug magnet.
Looks to me like Clutch material or Water.
Another thing , leave it for a week and see if any water comes to the top " Could be a water pump seal "