Very concise, however there are at least 4 heap allocations here from creating new strings.
This solution should not be listed best practice.

Fire all the pancakes and send OP to culinary school

This is a clever use of Linq, however it's poor performance due to needless heap allocations and iterates over the array multiple times.
This should not be marked best practice.

How many heap allocations does it take to screw in a lightbulb?

? operator short circuits None from inside the reduce closure if the i64 parsing fails in the map closure.

Ok fair enough

These kinds of Katas should always pass for correct answers, even if it sometimes passes for incorrect ones.

Best practice solution occasionally fails. Tests should be more lenient.

Nice!

haha

You certainly can :)

Thank you, thats very helpful!

I can see that the theme of the kata you referenced is different, is it only the kata implimentation that must be unique?

Love this one!

nice one liner!