はともかく・ならともかく: the difference
はともかくN2
Meaning
Setting aside, Apart from
Past papers
Tested once in past papers
Example
冗談はともかく、そろそろビジネスの話をしよう。
All jokes aside, let's get down to business.
ならともかくN2
Meaning
If it's
Past papers
Tested 3 times in past papers
Example
生魚ならともかく、納豆は食べられません。
If it's raw fish, sure, but I can't eat natto.
How to tell them apart
「〜はともかく」: after a noun, about an existing fact: 'leave the first, look at the second'.
「〜ならともかく」: after a supposition: 'if it were that special case, fine, but the reality is this, which is too much'.
The meanings are completely different; exams often list them together as wrong options.