Hello Christian,
Since the time zone corrects itself after Windows Update but later reverts to CST, I would investigate Windows Location Provider and any management policies that may be changing the setting. First, verify that the Auto Time Zone Updater service (tzautoupdate) is running and not disabled. You can check it with Get-Service tzautoupdate in PowerShell. Confirm that Windows Location Services is enabled and that the Windows Location Provider policy is not disabled under Computer Configuration → Administrative Templates → Windows Components → Location and Sensors. If the device is managed by Intune or domain policy, check whether any configuration profile or script is enforcing CST. Since the issue started after international travel, test whether Windows is receiving stale or incorrect location information by connecting to a different network, such as a mobile hotspot. Also, check Event Viewer around the time the time zone changes to identify any related location or policy events. Please confirm the Windows version, whether the device is Entra ID/domain joined or Intune-managed, and whether the change happens during active use, sleep, or restart. I would avoid disabling automatic detection or using w32tm /resync, as time synchronization does not resolve an incorrect time zone selection.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!
HP.