Hello Mangi,Balaraju,IN-Chennai,
Welcome to microsoft Q&A, thankyou for posting your query.
Technically it is possible to use existing subnets, but generally it is suggested to use separate or dedicated subnets for each ARO cluster to avoid potential conflicts.
Check and make sure that CDIR BLock (IP addresses) does not overlap with existing cluster.
Create and review the network security groups to ensure smooth traffic flow between the clusters.
Check if the subnets are configured correctly for service endpoints, routing, and DNS settings that the ARO cluster need.
Using the same subnets increases the risk of IP conflicts and operational issues.
Troubleshooting might become more complex with shared subnets.
Hope this helps you.