Book or online source on modern Linux system files and organization

[Bruce Labitt]

Feeling like a bit of a fossil and not knowing what files do what, or 
where things are located.  Need to fix an obnoxious problem with a 
keyboard and realize I just don't know even how to investigate this 
anymore.  What are recommended sources for a modern overview of system 
files, purposes and organization?

Think my laptop now believes my Logitech keyboard is the default 
keyboard.  This is bad, because it has a different number of keys and 
the mapping is different.  This a royal pia.  I am typing with a mouse.  
Even the space bar doesn't work.  Practically it makes a laptop into a 
desktop system.  I don't even know where to start since a lot of the 
Linux cheese moved, in the past 10 years.

System76 Oryx 6 Pro laptop.  POPOS 22.04.

Any tips or pointers to well written overviews on the modern 
organization would be appreciated.  Perhaps I could learn enough to at 
least know the correct search terms.

TIA, Bruce