Hello Maciej,
Thank you for posting question on Microsoft Windows Forum.
Based on your query of being unable to find any actual documentation for 'Windows Server Backup' Event ID codes for Windows Server 2016 and newer.
Well! Microsoft’s old TechNet page (the one you mentioned ) might be the only official Windows Server Backup Event ID's full list that people find. Until this moment, there is not a single, updated Microsoft page that publishes a neat, expanded Event-ID dictionary for Windows Server Backup for 2016/2019/2022 the way the old document did for 2008 R2.
Nevertheless, the backup service still logs to this path Applications and Services Logs → Microsoft → Windows → Backup → Operational and the same set of common Event IDs is what monitoring and troubleshooting tooling uses today.
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- This log contains most of the backup-specific events for Windows Server 2016+.
For a reliable reference. It is recommended to run test backups on your environment, export the Backup → Operational log, build a custom mapping of Event IDs to backup states and cross-check with VSS logs for deeper error analysis. This way, you will have a tailored Event ID reference for your specific Windows Server version, since Microsoft has not provided one beyond 2008.
Hope the above information is helpful! If it is. Free feel to hit "Accepted" for benefitting others in community having the same issue too.