You can transfer an entire subscription to another tenant (if it is not a CSP subscription) so an option here is to first move the resource group to another subscription first (a temporary subscription perhaps) https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/move-resource-group-and-subscription and then move this subscription to the new tenant - https://learn.microsoft.com/en-us/azure/role-based-access-control/transfer-subscription
This is usually the easiest way assuming your resource types support a tenant/subscription move at all.