Both CDK and TF are really bad dealing with several apps spread over different repos that share resources (e.g.: ECS Clusters, VPCs, etc...).
I had good experience by going a submodule route. One multirepo containing a CDK infra submodule and multiple repositories as submodules which each output resources (lambda code, etc.) which in turn can be imported more easily by cdk.
That said, I like how K8s + YAML allows a more "self service" like approach to IaC.
In my org the goal of our devops team is to specify some common patterns for applications, then allow devs to use themselves.
Both CDK and TF are really bad dealing with several apps spread over different repos that share resources (e.g.: ECS Clusters, VPCs, etc...).