Baffled by lack of transit from SeaTac

I grew up in W Washington, so I’m not a total noob about the (in my opinión) crappy mass transit options in our region. I left for 8 years and stupidly hoped that it would have improved, but here we are:

I cannot find a rapid or light rail option for me to get from SEA to downtown Tacoma. I am honestly stunned that in 2023, I cannot travel from one of the largest airports on the West Coast of the United States to the center of the second largest city in the metro area. I just want to avoid a $80+ Uber ride!

Am I the only one that finds that just…a bit bonkers?

Anyways, does anyone here have experience with the “Flix Bus”? Or am I overlooking another possible option? Do they have Uber Pool options from SeaTac?

Thanx in advance for any advice and apologies if this post is redundant.

Edit after all the kind and helpful feedback: thank you! Will definitely be giving the 574 bus a go.