The debate about whether or not an employer withholds taxes is beyond my area of expertise.
I did find the following 2 links that discuss reporting RSUs.
IRS Site: https://turbotax.intuit.com/tax-tips/investments-and-taxes/how-to-report-rsus-or-stock-grants-on-you...
Not IRS site: https://www.thecompensationconnection.com/2020/07/06/[product key removed]-payroll-tax-administratio...
I recommend talking with your employer and discussing withholding with them, likely the payroll administrator. However, if your employer does not withhold the proper amount, or if they don't withhold adequate FICA taxes, you will likely need to file quarterly estimated taxes. If that is the case, my previous comments on how to calculate these quarterly estimated taxes apply.
I am copying @VolvoGirl , who I have found to be very knowledgeable, hoping she can add her expertise to this discussion, or refer it to another expert.
