Instant custard cream

I would like to ask, if it is possible with a 60-65% moisture, to drop down the aw, below 0,85, of an instant custard crema, cold mixing.
I have achieved a perfect ph value of 5, so I am ok with that.

typical ingredients

modified starch
cellullose
alginate
sugar
maltodextrin
aroma
color
water
whole milk powder
sweet whey powder

I have used glycerine&sorbitol and inverst sugar to drop down till 0,90 but i want it to get down even lower. Sweetness is calculated at 15-16%

Theoretically, don’t see much more to dramatically drop Aw to your target.That formulation is laden with large molecules with no water activity depressing effect.Plus the high moisture content in the end product. .
If its okay with you.try replacing your sugar with a combination of monosaccharides and disaccharides.
Say 50 to 60% crystalline fructose 30 to 40 % dextrose powder and 10 to 20% sucrose. .Use it in combination of humectant like glycerol and sorbitol and measure the resulting water activity of the end product.
Fructose had more effective Aw lowering effect than invert syrup .
90% fructose syrup is also effective but not as common as crystalline fructose.
FYI Glycerin is much more effective than sorbitol in Aw lowering effect .Increasing the glycerin content in relation to sorbitol might help.

The ingredients may not be your problem right now from all you have listed above maybe it’s the mixing ratios. You can also try adding lecithin to your mix.