Sweetener syrups are now available to use in place of sugar and you can also make your own using a powdered sweetener in the same way you'd make a sugar...
I use pure allulose for my sunlike syrup or what you call sugar syrup and I also make my honey syrup using a sugar free honey alternative that is only available in the US and possibly Canada being modified Atkins. However, I will use liqueurs even though they have a ton of sugar and I’m going to use a sugar cube or Demerara sugar cube for making the Sazerac because it’s traditional to do that. I do wish people made sugar free liqueurs that used allulose so I can feel better about using them.