I'm sorry to hear of your confusion.
The term resident refers to your legal right to reside in the US. While you may be temporarily living in a foreign country because that is where your employment takes you, you are still a US citizen, must pay income tax on the income you earn there, you have property in the US and you are legally a resident of the last place you physically lived in the US unless you intend to be a legal resident of another state or country.
You may use your assets and income---from wherever derived, to invest in US securities.
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