@JakubMlynarczyk
Thanks for your posting on Q&A.
Perhaps you have missed the case. The case posted by CC yvan have the same configuration. Please review the thread first and confirm whether it is helpful.
Case link:
https://learn.microsoft.com/en-us/answers/questions/698128/wsus-sql-choose.html
In addition, I found a related Article to share with you:
https://www.serverwatch.com/guides/what-database-options-are-available-with-wsus-page-2/
Note that the link isn't from MS, just for your reference.
Best regards,
Rita
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