Portland is a pretty unique place. They famously drew a circle around the city and said development can’t go outside of that area which forced a certain density and allowed transit to be planned well in advance.
I didn’t spent a ton of time there and admittedly it was January so it was quite frigid, but the distances can still feel quite long between things outside of downtown. Portland made a few mistakes when they embraced car culture including getting rid of their street cars like many American cities. They also annexed a lot of less walkable areas around the city. There is no subway and the light rail seems well run but it doesn’t exactly cover the whole city. My sense is that most people who want to walk will end up biking or taking some form of transit in many neighborhoods because of the distances between things. In the winter it was quite hard to find lively streets and public squares to be quite honest. I suspect it’s because it’s easier to just drive when it’s cold, things are a bit far, etc.
Marin is lovely but most of it is extremely spread out. There are a few towns like you mentioned that one could conceivably get by without a car but it’s not easy. Looking at San Rafael, Google Maps shows 4th street is a walking area (denoted in beige) and a very small area a few blocks south near the Safeway around 1st and 2nd streets but it isn’t a very big area. Usually a giant chain supermarket is a pretty clear sign that things were designed for cars and not for pedestrians who would typically be better served by neighborhood markets and small shops near their house to grab some essentials. Zooming in near the walkable areas of San Rafael, Google Maps instantly highlights many car oriented businesses like at 2nd street and D street where we see a Chevron gas station, an Arco gas station, and an O’Reilly Auto Parts store all on one corner. I don’t know about you but even if it’s technically walkable that’s not what I want to walk through every day when I go outside especially if I need to walk past it to get to the train to commute to work, etc. A major highway cuts through the east side of the city which also limits expansion of pleasant walking areas and litters the area with on-ramps and other car-centric design.
Marin county famously blocked BART from expanding north in order to keep out the “riff-raff”. These sorts of decisions had major consequences and while you can find a few blocks here and there that are walkable, the county as a whole is largely long drives through tree covered asphalt in order to get between areas.
If you’re happy with a few blocks of downtown then admittedly some of the towns probably meet your needs but it’s not exactly designed for most people to live a car-free live. Even the Bank of America ATM there proudly shows on Google that it’s a drive-through ATM which I’ve never seen once in Europe (or San Francisco for that matter)