Mass timer buildings are prefabricated structures made of (hopefully renewable) wood. The pieces are made in a factory and then able to be quickly constructed together on-site.
This can hopefully greatly reduce the amount of carbon in the atmosphere from producing a building. The cost of producing buildings in this method is also going down. Additionally, these mass timer buildings are typically more dense than single family homes, which can lead to more sustainable communities.
Some issues are solvable with better architecture but developers don’t make money on it, many only build for the landlords. Stuff like good soundproofing between separate units, both a lift and multiple staircases in bigger buildings, visual variation between buildings or parts of buildings so people don’t get lost or stir crazy, outdoor spaces with both vegetation and useable areas.
Depends on your city, but many need more medium-density, not go straight from terraced housing to seven floor buildings.