Fully Support

Yep, fully support 20mph, or less in residential areas. In fact we should be deprioritising cars altogether and reclaiming streets for pedestrians & people who live on them.

However in places where there is already a 20mph limit it is largely ignored by many, who think they can get away with it, and they do.
So, in order to make this meaningful & for it to work, all 20mph limits should also be supported by measures to enforce them, whether that be speed ramps, street furniture, different road surfaces, road narrowing or whatever.
Simply sticking up 20mph signs and hoping that's the job done would be naive.