"sus" short for "suspicious," often linked to the video game Among Us which became very popular during the pandemic. I'm not sure if that was the origin; the Zoomers seem to like their abbreviations ("rizz" being short for "charisma" is another example) but Among Us definitely popularized it.
Idk about everywhere else, but “sus” or “suss”has been common slang for “suspicious/suspect” in Australia, the UK and New Zealand for at least several decades.
No. Sussed out, means to work something out. Usually implies a certain amount of trial and error, or coming to the realization slowly, depending on the context.
So, "I sussed out how to work the printer".
Sus, in British English didn't really have any meaning until the game came out.