For a 2022 backdoor, you would be entering the nondeductible new contribution on line 1, and the basis amount that already exists is line 2. That gives line 3 a total of basis in the Traditional IRA account.

The total converted isn't this part.

"The client strted in 2019 to 2022 total contributed 4X$6000=24000"

Then you don't really have a "backdoor" from the perspective of Backdoor. You have a partially taxable conversion, most likely, because their funds from 2019 and later were sitting there generating earnings, right? That means any conversion now, even if the same amount as what was put in for 2022, is a pro rata conversion.

Unless you are describing that every time they put into a Trad IRA, it was nondeductible and also immediately converted in full to Roth, and your "4X" is activity, not running balances?