Is there a way as an admin to restrict who shares with who, other than isolation through Namespaces?

I have a scenario where I would like to restrict who can share with who in our QuickSight environment.
As an example, I have three groups of users - Group A, Group B, and Group C. Here are the groups that I want to be able to share with each other:
A, C
A, B
But I do not want C and B to be able to share with eachother.
Is there a way to achieve this sort of sharing restriction?
I know that sharing can be prevented by isolating users in Namespaces, but separate Namespaces would prevent A from sharing with B and C as desired.

For a little more background, the reason that we don’t want B and C to share is that they should only have access to different sets of data. We give them access to different sets of data at the Author level by using IAM policies. However, sharing overrides these IAM policies (e.g. if B shares it’s data with C, C can now see the data from B that it shouldn’t have access to according to it’s IAM policies. See this post for more info: Sharing Overrides IAM Policy Permissions - Is that intentional? - #5 by agmayan).
These requirements and the observed security behavior are what lead to the question around restricting sharing.

I don’t believe this is achievable. To my understanding either you would be able to share with all or you would be able to share with none.

I would suggest opening up a case to see if AWS could make an exception or give you an option to be able to do that.

Here are the steps to open a support case. If your company has someone who manages your AWS account, you might not have direct access to AWS Support and will need to raise an internal ticket to your IT team or whomever manages your AWS account. They should be able to open an AWS Support case on your behalf. Hope this helps!