>Java also could not fix it (which may be one of the main reasons behind Kotlin).

C# added some null-safety features despite having a 20-something year baggage of legacy code. While it might not be the perfect solution (these checks work only at compile time and you can enable them per-file), I find that they work great for new projects. You have to be extra careful at boundaries (interfaces with third-party libraries which have not added ? annotations yet, API calls, and so on), but they save a lot of headache inside your own code.