What is the ruling on benefiting from the 401K retirement savings plan invested in shares of American and international companies, and how is Zakat calculated on it and on the retirement savings account, given that there are penalties and taxes for early withdrawal?

Retirement and social security funds can be permissible or impermissible, depending on the nature, purpose, and conditions of the fund. The savings plan mentioned in the question is highly likely to lack Sharia-compliant controls, thus it is not permissible to subscribe to it. It is permissible to benefit from it to the extent of the monthly deductions from the salary and what the company grants, in addition to the profits from investing the funds in Sharia-compliant ways. Anything beyond that is not permissible and must be disposed of by spending it on charitable causes or giving it to the poor and needy. One should examine the nature and methods of stock investment to determine what is permissible and what is not. As for Zakat, it is not obligatory until the money is received and taxes and fees are deducted. The money is then subject to Zakat for the past years once it reaches the nisab.