For development/testing environments where you need multiple RDP sessions without paying for RDS CALs, consider using (which allows unlimited RDP sessions when patched, but still violates EULA) or better, nested virtualization with properly licensed evaluation copies.
Older patching tools (e.g., Universal Termsrv.dll Patch v2.x) often failed on Server 2019, leading to blue screens, boot loops, or simply being reverted by SFC. Termsrv.dll Patch Windows Server 2019 REPACK
Modifying core system files like termsrv.dll is for production environments due to several critical factors: but still violates EULA) or better