I download Pub 15-T to see what they did with the withholding tables. It has both the old W4 method and the new.
The old W4 is basically the same with a standard deduction of 3,800 for single plus 4,300 per allowance, so that claiming single 2 gets you to an annual exclusion of 12,400, exactly the 2020 standard deduction.
The new W4 tables don't have an annual table, so I used the monthly table for single without the 'two jobs' box checked on the W4, and the standard deduction amount is 1,033. Times 12 = 12,396. If you check the box for two jobs, it cuts the standard deduction amount in half (517 x 12 = 6,198).
I wish they had built a little cushion into the new tables by using, say 10,000 for the standard deduction because I'm afraid this is going to cause a lot of people to be under withheld, especially hourly workers with varying hours.
I'm going to recommend that people enter extra withholding on the new W4 more often than not, so they don't get mad at me when their refund is a lot smaller or nonexistent.