The nonresident withholding is a distribution. It is not deductible on the 1120S. The whole point of making the PTET election is so it can be deducted on the pass through entity's federal return, bypassing the $10K SALT limit that individuals have.

The shareholder can deduct the amount of the nonresident tax withheld on their share of the 1120S K-1 income on their Schedule A Itemized Deductions to the extent it was paid in 2022. If paid in 2023 they get a 2023 deduction. Their Sch A deductions are subject to the $10K limit.