Earlier quoted context omitted.
But the problem is that checked exceptions create the same “what color is your function” problem for errors.
It isn't? You have a function red that doesn't throws anything you use a function blue that throws checked exceptions you handle the exception and it's all. The red functions doesn't become blue.
map it to another checked exception and you now have a "blue" function. and, you also have another layer of abstraction in your errors.
if you can't actually handle the error, skip the circus and just let the exception propagate to a general error boundary (alongside all those RuntimeExceptions you're unaware of).
It's a deep ocean, your defense mechanism of guarding against Checked Exceptions is a small fraction of all exceptions.
To be fair, I did really like the idea of checked functions when I first started using Java. But in practice, it's just too hard to tell what operations should be Checked / Unchecked (sometimes).