scozic that is true. Access to Windows Server services like Fileshare or Domain Controller always requires CALs.
Important to note, there exist other licensing terms and products that suffice the requirement for Windows Server CAL.
Examples:
1. Windows Server Datacenter running on Azure Stack HCI through Azure Hybrid Benefits.
Why: Running Windows Server VMs on-premises using this Azure Product has the same benefits as Windows Server running in Azure VMs.
2. Some Microsoft 365 plans include so called CAL Equivalency.
This covers Windows Server CALs (and other Office Server CALs) for licensed M365 users. RDS CAL are not included, however access to Azure Virtual Desktop is covered.
You can find an excellect overview here: https://www.microsoft.com/licensing/terms/en-US/product/CALandMLEquivalencyLicenses/MCA looking for Microsoft 365