If working abroad, the good news is the IRS allows for “Foreign Earned Income Exclusion”(FEIE) of over $100k in 2021. This is great when working in low tax countries such as UAE, Qatar or Saudi Arabia. There are also Double tax agreements that allow taxes paid to foreign governments be deducted from your overall US tax obligations. By waiving your FEIE, you could qualify for tax credits, such as the Child Tax Credit, some of which is refundable. Using a professional tax service is highly recommended to navigate the exact rules and filing requirements for receiving tax credits, stimulus checks, or if you qualify for a refund!
Note: there are some countries that tax worldwide income, similar to the United States. Each country would have their own filing requirements and guidelines. Best to do some research to see if you are affected when working outside of your home country. US citizens are required to file their tax returns every year, even if living abroad.