Can you substitute sliced apples for jam? Thinking it might make a nice Apple Sq for the Jewish holidays.

Elcookie, I think the apples will work but/and be aware of some changes that will result from repkacing the raspberry jam eith tham:
The bars will be less sweet (maybe ok with you; if not add a tbsp or two of sugar)
They will be moister bc the apples have more water than jam ( lift ok, dobnithing; if not ok, add a little more iats).
The fish will lack the bite (slight acidity) of the raspberries. Add a bit of lemon/lime juice or balsamic vinegar.
Shana tova,
Nancy