If COBOL is still relevant, does that also mean in 5-10 years we have ancient Java 4, dotnet 2.0 and node.js systems that need to be taken care of - or do systems built on COBOL and similar run in a timeless vacuum and there are really not much more like that?

I’d expect the same for old Java/.NET projects, although COBOL stuff does to have dinosaurian longevity - other tech seems to just get replaced/rewritten much more frequently.