Sounds like you lived in Oregon for 2020 if you have not moved to Texas yet. File an Oregon tax return. Moving to Texas in 2021 does not affect your 2020 tax return.
But if you will be moving soon, use the mailing address on your tax return where you want to receive mail from the IRS.
For tax purposes, you don't become a resident of TX until you begin living in your new permanent home in TX.