Restricted Stock Unit (RSU) Basis and Shares Withheld for Taxes

I had 100 Restricted Stock Units (RSUs) vest with 30 RSUs withheld for taxes on 2/15/23.  The net 70 shares were made available in my brokerage account on 2/22/23.  My question is if my basis on these net 70 shares (for when it comes time to sell them) is the stock price on the vesting date of 2/15 or is it the price on the 2/22 date that the shares were available to me in my brokerage account?

Also, is the withholding of the 30 RSUs for taxes considered a stock sale which should be reported on my 2023 return, or is it not considered a stock sale as RSUs were simply withheld and never owned by me?