The instructions don't cover the case of an empty input string well enough.
From the description I would assume that rule number 5 applies (because all other rules don't match and because an empty string has no vowels).

The equation in the kata description is not displayed properly:

It depends on the language. In English, it can be both a vowel and a consonant. In some countries, it can only be a consonant.

Nah, I think 6 is more suitable.

No random tests.

Ruby 3.0 should be enabled.

This was a good kata, though seems a bit tough at 6. I'd think 5?

Please use new python test framework.

Link needs to properly inserted.
Wikipedia link states:

When referred to as the divisor function, it counts the number of divisors of an integer (including 1 and the number itself)

and here:

where σ is the divisor function (or sum of all divisors)

Clearly sum != count, that needs to be fixed.

added

Read this, see the error message, it tells you exactly which assertion your code is failing.

Not an issue of this kata.

Not an issue.