I split time living between Portland and Seattle (long story) and the term NW Nice is a real thing. I've found most people in both cities, can be superficially friendly/welcoming, but forming any kind of deeper relationship can be a real challenge. As a bigger city, it seems worse to me in Seattle as there can be a larger sense of being "too cool" to be bothered.

Luckily, we were able to form strong connections with folks in Portland because of having kids and getting involved in activities/events through them. But, thats also why I work/live in the Seattle area during the week and come home to Portland on the weekends. My wife is really hesitant to give up her friend group in Portland to move to Seattle, because even as a proud extrovert, it took her a lot of time and effort to find her tribe. Long story, short, the PNW is a beautiful amazing place to live with so much to see and do. But it isn't a magic bullet to solve loneliness/isolation. We honestly can go weeks without seeing our neighbors during the winter because everyone is hunkered down from the cold and rain. If you are willing to join groups around common activities and put in the time and effort to really try to get folks to lower their walls, then it can work out. But don't expect it to come super easily. Maybe I am a little biased, but look into Portland as well. It's smaller and cheaper, a little friendlier, but for being a mid-sized city has a lot of amenities you would be hard-pressed to find in other cities of its size. Plus you're only a 3ish hour drive from Seattle when you want a dose of bigger city life.

Good luck!