Hello
Azure RBAC permissions are inherited and the combination of all permissions a user is assigned at a particular scope. You cannot exclude a specific permission at a lower scope (for example a resource).
If you want to exclude access to particular resources, then create them in a different container which the user doesn't have that level of access to. (For example if the user has contributor permissions on the subscription, put the other resources in a different subscription). Further information can be found in our best practices.
A better approach would be using the zero trust principals and not grant that user explicit write permissions to the subscription, instead add it as an eligible permission in Azure Privileged Identity Manager and enforce approvals for the requested scope. (For example they may be eligible for contributor at the subscription level, but request access at a resource group)
kind regards
Alistair Ross