The L&C universe doesn't show us anything more advanced than the Globe.
Well, you do have Clark’s ship that was able to navigate to earth, unless Jor-El was able to compute everything with omniscience, it’s AI had to be able to make some rather advanced decisions. And you have the transport Ching and Zarah used: “imagine an entry and you find one” The glasses of liquid that simply appear, seemingly at Zarah’s mental command etc.
But that is beside the point it isn't just loss of knowledge, it is a LACK of people to fill the roles.
Not necessarily, In L&C the kryptonians seem like a strange mix of primitivism and advancement, so I there isn’t any canon I think you will ignore.
But there are many Science fiction visions were people doesn’t need to use or understand their tools, the tools themselves are smart enough to anticipate their needs. Like in say ASIMOV robot stories where the AI takes the power because it realizes they it is far more suited to rule humanity then humanity itself. In Stark Trek you have the replicator technology that allows you to turn your garbish into a steak, or a sofa, or whatever, no one needs to do any real work or understand the process anymore then we understands why the lightbulb shines when we flip a switch.
