Can Yanjing Flower City in Yantai Development Zone only use Unicom's broadband?

Generally, there will be multiple broadband operators in a community. Unless the residential property signs an agreement with an operator, other operators are not allowed to stay, otherwise there will only be one.

You can directly ask what broadband can be installed in the residential property, or check what broadband publicity activities and broadband boxes are available in the residential area. You can also ask your neighbor which broadband is installed to judge.