I'd guess they live (and work) in Washington and shop in Oregon.
That too for sure, but the number of cars with WA plates that can be seen downtown during the workday and the rush hour traffic flows on I-5 indicate a lot of working in OR and living in WA. Of course that's down somewhat since the pandemic. There's also a Clark County express bus line to downtown Portland that makes five trips an hour plus several other bus routes to downtown and the OHSU medical center.
People who live in Washington and work in Oregon do have to pay Oregon income tax. But even with paying OR income tax it's still much cheaper than living in Multnomah County (home of Portland) which has the highest (or very close to it) income tax rate in the country. These high taxes combined with a feeling of a distinct decline in the quality of life in Portland have driven quite a few people to move across the river or into surrounding Oregon counties with lower tax rates.
Here's a story about the decline in tax revenues that Oregon received from Clark County residents after the pandemic hit.
People working for Oregon employers generally don’t have to pay the state's income tax if they don’t come to Oregon to do their jobs.
www.oregonlive.com
Here's a story about Clark County's "sales tax leakage" to Oregon. It also mentions that people live in Washington and register their cars in Oregon and/or maintain their Oregon registration when moving North. Shows what I know!
Clark County’s sales tax leakage, the government revenue lost when locals head to tax-free Oregon for their shopping, has been on the decline for the last few years, according to County Finance Direct
www.columbian.com