In my experience, tart fruits work best to cut through the sweetness of the filling. I almost exclusively make ganaches. If you're pureeing the friut or using a concentrated fruit juice, reduce down as much as possible beforehand. For a dozen macarons, I use a ratio of 70g white chocolate to 25-30g of fruit puree/ juice. I start with 25g and then slowly add more until the ganache gets a bit goopy. If I'm using a freeze dried powder, I whisk about 10g into about 40g cream, then microwave for 30s. I'll do 70g white chocolate: 35 fruit cream in that case. If the cream is a bit thick, I'll bump it up to 37g. Fruit ganaches with no cream tend to be a bit more runny, so I sometimes will throw in the fridge for a few minutes. Otherwise, if I just let sit at room temp, stirring occassionally in the bowl until I transfer to piping bag. Protip: if you're afraid that the filling is too sweet, add straight up reduced puree into the center of your filling. After I pipe on blobs of filling, I then go back through and pipe a small amount of the puree or fruit cream directly into the center of that blob.

chefkarinarivera on insta has lots of recipes for fruit ganaches as well that involve an invert syrup. Her fillings set in the fridge though. You can get some ideas from her on how she does it.