That's a very loaded question that's diffcult to answer without not really answering it 😞
The answer is that it depends on
your sales process/cycle
definition of touch (are you counting all marketo emails, including automated? calls? demos? etc, etc)
lead source and history
size of deal
and many other considerarions
I would try to reduce to scope of the question to smaller chunk, like: how many touches to get a hold of someone? I feel like I've seen stats on that. Or more generally try to pick only the part of the sales cycle that you care about - at least it will be measurable....
I was on a call recently with an analyst firm in the B2B tech industry discussing cold calling metrics, and their guidance was that after 10 touches we should expect about 25% of prospects to engage in a call. Touches in this case meant a combination of email and phone.
So 40 touches to get someone on the phone to talk about your offerings.