Does switching to an Azure Plan affect my existing resource groups or deployments?

No — switching the billing/subscription type to an Azure Plan does not move, delete, or reconfigure your existing resource groups, VMs, databases, or deployments. The migration is a change at the subscription/billing level; your actual deployed infrastructure stays exactly where and how it is.

It's still good practice to coordinate the timing of any subscription-level change with your team, in case of unrelated maintenance windows, but the migration itself isn't expected to cause resource downtime.