what is actually salvageable?

hello! im new here, i am just getting into computer science its super interesting, i am very big on diy and repurposing even just for passion projects, it would be super cool for me to learn more about tech through a creative outlet.

however... i keep seeing people say that cyberdecks (not all wich is fine and dandy) are often put together with salvaged/thrifted parts but i cant find anyone clarifying what that means! I would be totally cool buying a rasberry pi and sd card if i knew that i can scavenge the other parts for cheap, can you really do that and how do you go about it?

can a moniter/screen be disconnected from a device and reconnected to a rasberry pi? are powerbanks easy to find? how do you know if they are compatible? is a cooling system needed and found easily?

my biggest ask is basically is there anything reusable for a cyberdeck that you could find from taking apart older electronics (computers phones etc) or easily found at the thrift.