If you have no income from US sources after leaving the US, you would not need to file form 1040NR as you would not have any income to report. Although, you would technically be a Dual Status Alien, you would not have anything to report during your status as a non-resident if you choose to terminate your residency when you left the country.
Since you left the US in July of 2023, if you select that date to terminate your residency, then you would only need to file a return that included income for January through July. Then with no US source income after that, your reporting requirements would end for 2023.
Yes, you would need to attach a statement to establish your residency termination date. See page 13 of Pub 519
If you chose to be a resident for the entire year, you would need to figure out a way to get the numbers for the income you earned in 2023 from the foreign company. Your foreign company would not create a form that fits with the US returns, so you don't necessarily need a form, just the numbers of what you earned.
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