use of 172.17.0.0/16 in a subnet of my VPC , does it affect other subnets in my VPC or other VPCs I am connected to it?

Hello.

According to the Cloud9 troubleshooting document below, it seems that if you start with CIDR "172.17.0.0/16", you may not be able to connect.
Basically, I think that only the "172.17.0.0/16" VPC will be affected.
However, I think that communication from Cloud9 to "172.17.0.0/16" will be affected, so I think it is basically a good idea to avoid using "172.17.0.0/16".
https://docs.aws.amazon.com/cloud9/latest/user-guide/troubleshooting.html

Issue: For an EC2 environment, if you launch the EC2 instance into an Amazon VPC that uses the IPv4 Classless Inter-Domain Routing (CIDR) block 172.17.0.0/16, the connection might stall when you attempt to open that environment.

Cause: Docker uses a link layer device called a bridge network that enables containers that are connected to the same bridge network to communicate. AWS Cloud9 creates containers that use a default bridge for container communication. The default bridge typically uses the 172.17.0.0/16 subnet for container networking.

If the VPC subnet for your environment's instance uses the same address range that's already used by Docker, an IP address conflict might occur. So, when AWS Cloud9 tries to connect to its instance, that connection is routed by the gateway route table to the Docker bridge. This prevents AWS Cloud9 from connecting to the EC2 instance that backs the development environment.

Recommended solution: To resolve an IP address conflict that's caused by Amazon VPC and Docker using the same IPv4 CIDR address block, configure a new VPC for the instance backing your EC2 environment. For this new VPC, configure a CIDR block that's different from 172.17.0.0/16. (You can't change the IP address range of an existing VPC or subnet.)