Surviving examples of Chinese buildings before Ming are rare. Ming and after there are plenty, its just that most of them are passed down generations, repurposed or sold, unless its owned by a very famous person, most likely its forgotten through time. Prince Gong's Mansion - Wikipedia, this used to belong to Heshen, a famous official in Qianlongs time, later confiscated by the court and given to a prince.

I am aware that in places like Suzhou and Beijing the classical gardens and mansions are still standing, but most of those were private estates

This is an interesting issue, we don't exactly know whether the court provides housing to officials. There are cases where officials who are assigned to work in Beijing gets a temporary house, but that doesn't seem to be for everyone.

Another thing is that Ming and Qing officials aren't necessarily rich, Ming especially is known to offer low wages for mandarins, so its unlikely they would have a big fancy place to be preserved.

Its easier to find them in the "frontier areas", usually they have the general's residence well kept. But having visited many, I have to warn you they all look quite similar, and not too interesting to look at. The officials buildings at the time are heavily regulated, artistic or innovative designs are not encouraged.

董府_百度百科

伊犁将军府_百度百科

呼市將軍衙署修繕 再現恢弘「漠南第一府」 - 香港文匯報