I have not lived in the United States since 1990. Do I have to file a state return?

State laws generally dictate that you retain your state domicile even out of the country, until you take positive steps to change your domicile.

Such steps might be: getting a residency visa in a foreign country, registering with the local authorities of your new living arrangements, filing official documents with the local authorities of your intention to relocate there, and so on.

In other words, you have changed your domicile when you have moved somewhere else with the clear intention of staying there and not returning to the state you used to be in.

Once your domicile is no longer in a state, you no longer have to file that state return.