C arrays are syntax sugar over pointer arithmetic and defining up a handful of FORTH words to do the same thing (plus a bump allocator) is sufficiently trivial that putting it in core would be weird, because -in general- FORTH programs are low level enough you wouldn't have -many- dynamic arrays so having separate words for each one often makes a lot of sense.
This isn't to say that FORTH is going to be particularly -suited- to writing something like a todo app, and I'm having the sort of day where I can see the rough shape of the required code in my head just fine but cannot for the life of me convince my fingers to produce you a useful example, but it's very much doable.
Well then it's weird that no Forth programmer I've asked can produce such an example when I ask them, and instead tell me to use another programming language
They probably tell you to use another programming language because if that's the kind of questions you are asking for your todo list application using another programming language is likely going to work better for you. It's a bit like asking to provide the schematics for a particular type of wrench when your job is to put a nail in the wall.
This isn't to say that FORTH is going to be particularly -suited- to writing something like a todo app, and I'm having the sort of day where I can see the rough shape of the required code in my head just fine but cannot for the life of me convince my fingers to produce you a useful example, but it's very much doable.