Does a 2006 BMW 325XI have a timing belt or chain, and can a broken serpentine belt cause the timing to jump?

If the motor has a metal cover behind the serpentine belt it has a timing chain. If it's plastic it's a timing belt. I doubt that the serpentine belt can cause the timing to jump.

No a broken serpentine belt cannot cause an engine to jump time.

It has a timing chain - notice the metal cover behind the serpentine belt to keep oil on the chain instead of a plastic cover to keep dirt off a belt.

If there is a problem with the chain tensioner the chain could jump when the serpentine load suddenly disappears.

Hi the whole issue to do with timing belt jumping has nothing what so ever to do with the other belts in the car. yes they have worn as much if not worse. so in most situations this could be the end of this engine destroyed by lack of maintenance