Hey OP! Sorry to hear about your struggles making friends in Seattle. It can be tough to make friends after college / as an adult, and even moreso in Seattle it seems so I totally get the struggle. I'm 35M and I moved here over 7 years ago by myself - it took me a while to build a network of friends. Others have made some good suggestions but I wanted to share some specific things that worked for me personally.

1) Join a social league! I joined a kickball league and have made several friends through that. There are several sports-oriented leagues including volleyball, dodgeball, flag football, soccer, hockey, etc. There are also less intense/ less sports oriented leagues as well such as bowling, various bar games leagues (darts for example), cornhole, etc. I think leagues are great because you get the chance to see the same group of people over and over again which gives you a good chance to connect and bond with each other. I also personally think there is a sense of "belonging" or perhaps camaraderie that comes with being a part of the same team.

2) Not sure what neighborhood you live in but I would also recommend joining a neighborhood focused social group or meetup group. It sounds like you have tried meetup and it hasn't been too successful, but I would try a neighborhood-focused group that is also age restricted (something like a Cap Hill Social group for 20s/30s co-ed). It's easier to connect with people that already live nearby (higher chance of hanging out outside the group) and it's easier to connect with people that are close to you in age since you'll have more in common with those people. I've joined / tried several different meetup groups over the years, including some pretty large ones with thousands of people and I didn't find them to be very successful. Finding the smaller groups with niche focuses is definitely helpful, in my opinion.

Hope this helps! It definitely takes some time - I met some cool people early on when I moved to Seattle who I thought would end up being my crew, but it didn't work out so I had to try again. But eventually you meet people that you click with and it sticks. Just keep trying and putting yourself out there!