Can a Contributor create a policy that stops others from making changes?

Yes, a user with the contributor role in Azure can create a policy that restrict others from making changes

How can we check which policies are affecting what the Owner and Contributor can do?

We can check Azure Policy assignments, role definitions, role assignments, and RBAC conditions also...so we can identify which policies are restricting or affecting the actions that "Owner" and "Contributor" roles can take within specific scopes in Azure.

which act like a failover cluster ZRS? or GZRS? how?

ZRS acts like a failover cluster by keeping your data synced across multiple zones in one region for automatic zone-level protection, while GZRS adds protection by also copying data to a second region to handle full regional failures.

For a mission-critical application needing disaster recovery, which option is most suitable?

Which option is best for local cost-effective storage with no cross-region replication?