your current tax rate has nothing to do with what your tax rate would be if you cashed out your 401K. the entire distribution in excess of any basis you have would be taxable in that year. taxable income would go up by this amount and you will end up with some income taxed at a higher effective rate. by law, a minimum of 20% must be withheld from a 401K distribution. if you have too little withheld you could be subject to underpayment penalties.
you could use the 2021 tax rate schedule to estimate what you would pay in taxes on a total distribution.
https://www.irs.gov/pub/irs-pdf/i1040gi.pdf
