Symptoms
- Windows App / Microsoft Remote Desktop on macOS fails with error 0x204.
- Same PC reachable from Windows clients.
- New Mac setup or recent client update.
Fix it yourself
- Confirm Remote Desktop is enabled on the target Windows PC - the most common cause of 0x204.
- Verify the PC name/IP entered on the Mac is correct and the Mac can reach it (same network or correct VPN); if the name fails, connect using the IP address (and port) instead.
- Check port 3389 is open at both ends - the Windows firewall on the PC and any firewall on the Mac side.
- As a diagnostic, have the PC owner temporarily clear 'Allow connections only from computers running Remote Desktop with Network Level Authentication' and retest, then restore it.
- If the client itself misbehaves, remove its cached configuration: first confirm with the user (the folder holds saved connections and settings) and copy it somewhere safe, then move the 'UBF8T346G9.com.microsoft.rdc' folder in ~/Library/Group Containers to the Trash and reopen the client so it rebuilds.
- Retest the connection.
If that did not help
Attach the macOS and RDP client versions, the target Windows edition, whether 3389 tests open from the Mac, and the exact error code.