ROTH IRA or Taxable brokerage account?

Im 29 , earning $50,000 a year. Im an immigrant and just started working in the USA for 2 about 2 years.

I spent my first year building my emergency funds in my HYSA and as of today, i have saved around $20K. I also have a 401K which i only matched up to my employer's 6%.

I wanted to try investing my money but im not sure whether to do ROTH IRA or brokerage account. I am not sure if i will be retiring in the US and but hopefully i will have my US citizenship within the next 5 years.

Im not sure which investment would be ideal for me in the long run. I also wanted to have flexibility – i wanted to be able to access my savings easily in case i needed funds for big purchases such as a house, car or marriage.