Steve,
For more information on this topic see the Oregon Department of Revenue document "2020 Publication OR-17, Oregon Individual Income Tax Guide". Page 47 lists Oregon taxable income and provides a formula to determine total wages taxable by Oregon. And, yes Oregon taxes you on "income earned from work performed in Oregon, including sick pay and other benefits."
The formula essentially divides your days actually worked in Oregon by the total number of actual work days and then multiplies that by your total wages to come up with your "Oregon Wages". I called the Oregon Department of Revenue to ask for a definition of "Days actually worked in Oregon" because I had many where I began and ended my workday in my home office but went to Oregon for only a portion of the day.
You'll want to keep a record of full and partial days you work in Oregon in case you get audited. You'll also need a letter from your employer on company letterhead stating that you telecommute and/or travel for business outside of the State of Oregon.
