I also want to build a cyberdeck one day but from the quick research I did I think you don't only need coding knowledge, you also need hardware
It depends on what type of cyberdeck you want to build, if you want a super powerful cyberdeck then obviously you're gonna need a very good cpu and ram -and the costs ahem ahem-
So I think making more research on what type of cyberdeck you want to do "do I only want it to message people? Do I want it to do something else?" etc etc would be a very good step
Also keep us updated on your cyberdeck journey we would love to see that ໒꒱

you could buy a raspberry pi, hook it up to n external battery, add a compatible screen and a keyboard. then shove all that inside a 3D printed shell, if you can't design your own, you can probably find .stl files on the internet and modify them a little if you have to with the help of a youtube tutorial.
also, you don't need to know coding to use a raspberry pi, since you can just install android on them

well, the best starting point for a project like this is always a raspberry pi
Now, it depends largely on how complex you want it to be, and how "stylish" you want it to look.
In terms of complexity, another user pointed out you could install android on it but that defeats your plan to stop using your phone as much. You could always try to code your own OS but that's a bit much and there might be compatibility issues with apps you wish to use, especially if you go for a linux OS instead
On the stylish side of things, to make the frame look "professional" there's no avoiding a 3D printer, but you could just as well make it out of cardboard and it'll function the same.