Nodes have more than 8 connection slots, by default they have 125 maximum connections. There are 8 outbound connections, but can still have incoming connections from other nodes when all 8 outbound connection slots are full. So in your example, the new node can open a connection to any of the other nodes in the network because they all have available incoming connection slots.

Furthermore, because connections are classified as incoming or outgoing (but data is still bidirectional), at least 8 of the 9 nodes will have at least one more outgoing connection slot.

Also, your question has nothing to do with blockchains and is solely related to networking.