Help getting started

Hello! I am a programmer/IT professional but I'm interested in dipping my toes into hardware design.

I want to make a cyberdeck but am unsure where to start; the mobo, screen, periferals, design?

I want to use this to run a HMD with a basic ubuntu-style OS(browser, text editor, etc). If possible I would like USB expandability, an extra display separate from HMD, and fits in a arm or belt wearable frame.

So far, I have looked at raspberry pi zero 2 but they're hard to get. I don't see arduino being a good option for the power I want. Haven't looked into lattepanda or any of the other common boards.