My three gliders do not like fresh apples, dried apples, or apple sauce - seem to like apple juice not from concentrate and made from pressed HoneyCrisp apples.
Also, when I'm trying to encourage a new food or one they seem to only like part way, is to lace it with honey! Also, try cranberry sauce - it's tangy which they seem to love and hides the tastes of stuff they don't particularly care for.
Short term sweet foods they want to gorge on is fine, but long term sugary (ie sucrose - table sugar, a complex sugar) stuff is to be used very limited - fructose, a simple sugar, is best even long term, but don't be fooled by 'high-fructose' corn syrup... it's still dextrose (bad complex sugars). Fructose and honey (the REAL glucose) are the simple sugars and best for the sweet toothed little darlings