> only have a foggy idea how convenient working in modern C can be

Here is a list of C++ features that C doesn't have, that are an immediate deal-breaker for me:

  - reference and move semantics
  - templates, and type constraints with concepts
  - namespaces
  - `constexpr`, `consteval`, and other compile-time magic
  - `auto` type deduction
  - trailing return types 
  - RAII (can't believe I put this this late, but eh)
  - a passable (although still not perfectly complete) standard library that blows the C standard library out of the water
  - improved semantics that allow programmers to reason about the logic in code better, than obsess over pointer arithmetic
  - built-in virtual functions, function pointer tables, etc

I can list more, but this is going to end up as a list of 'essentially every feature in C++ that isn't in C', which is the very reason for the former language to exist.