Jam is mostly added sugar with some fruit — not toxic, but far too sugary to be a real food for parrots. Fresh fruit is the obvious better choice.
Keeper's noteSkip it in favor of the actual fruit. If a bird grabs a smear off your toast, it's not an emergency — just don't make it a habit.
What to watch out for with jam
Jam, jelly, and preserves are fruit cooked with large amounts of sugar (and sometimes pectin and preservatives). The result is a sugar concentrate that loses most of fresh fruit's benefits. It's not poisonous, but it's essentially candy in spreadable form.
How to serve it
Avoid as a food; offer fresh fruit instead.
A stolen smear is harmless but not to be repeated.
Never as a routine treat or medication vehicle (too sugary).