From all my travels and places I’ve lived while working, Lancaster Pennsylvania fits your criteria and is not exorbitantly expensive as are the major metropolitan areas.

Pro-LGBT, college town with a historic black college, major art college, the city has a high left leaning population, strong PSL branch, highly diverse with a healthy mix of various Black, Asian, Hispanic, and “ethnic” white populations. Fairly decent communal transport, good community support networks.

The Pennsylvanian valley area also has virtually no natural disasters. Maybe a tiny heavily weakened hurricane from down south will come through as a strong thunderstorm once every few years, but that’s all.

All around decent city. Reminded me a little of the smaller cities in Belarus.

In general, Pennsylvania is a commonly overlooked and very good choice, though some research is required as some areas are basically the Deep South, but those are easy to avoid.