Like many large US cities, and quite a few smaller ones, Portland has a shortage of affordable housing. And by "affordable", I mean housing that regular people (i.e., no trust fund, no six-figure salary) can afford without working three jobs or selling a kidney.
Rental stock in Portland ranges widely from old brick and stucco buildings of various quality, to modern, well-equipped high-rises.
ADUs (Accessory Dwelling Units, a.k.a., Mother-In-Law units) can be found, though until very recently, the red tape and expense of building them discouraged new construction.
Vacancy rates in recent years have been very low, which is not good for renters. However, the city has a reputation for certain renter-friendly policies.
If you can afford to purchase a home here (plan on, well, $400K minimum in desirable areas), more power to you.
Cost vs. location
Housing costs are not as obscene as New York City, Boston, or San Francisco. But you may still have sticker shock. As everywhere, costs are generally higher in the more desirable places to live*. Additionally, the further you live from the central, walkable areas of the city, the more your life may resemble that of someone living in any random U.S. suburb or poorly planned city. You'll still have access to all the natural beauty of the Pacific Northwest, but you may also spend a lot of time in your car.
* Note: I'm not addressing the suburbs here. Some of them are beautiful, but they are not generally known for being champions of the 15 minute city concept. Once again, back to your car.
Choosing where to live
Certainly, some people will sign a lease without visiting first, but I believe you will find a better lodging fit by visiting the city first, just spending some time walking and/or biking around different neighborhoods. Neighborhood feel can vary a lot from block to block. Additionally, chatting with people about neighborhood amenities, safety, noise levels, and demographic can give you a lot of information not readily apparent from rent.com, Craigslist, or wherever you are apartment hunting. Some apartment rental sites will provide a walkability score, or bikeability score, but this is better understood by actually visiting the building or neighborhood in question.
One weird trick?
If you make an account on Nextdoor.com in advance of your move, or check relevant Facebook groups regularly, you might spot a place for rent before it gets listed on the usual platforms. There's no guarantee here, of course, but you might get lucky with something.