Windows Server 2019 Standard reboots by itself

TL;DR: I would recommend check your hardware if your power supply is functioning properly or if CPU is not overheating to cause the computer shutdown since you didn't found any disks with errors, neither creates them.

Explanation:

You have two Events: 6008 & 41

Regarding 6008: Event ID 6008 entries indicate that there was an unexpected shutdown, as it says. If you press on one of the events with ID of 6008 it might say: "Critical thermal event" - Critical thermal event indicates that the problem is related to one of your hardware components not functioning properly that is triggering the computer to shut down.

Regarding 41 might not contain sufficient information to explicitly define what occurred but probably caused by 6008. Checking your Event both BugcheckCode and PowerButtonTimestamp are 0, this means that something prevents Windows from generating error codes or from writing error codes to disk. Something might block write access to the disk (as in the case of an unresponsive computer) or the computer might shut down too quickly to write the error codes or even detect an error.

More Information: https://docs.microsoft.com/en-us/windows/client-management/troubleshoot-event-id-41-restart