Hi @David Zemdegs ,
It is both possible and supported by Microsoft to perform in-place upgrades, the recommended approach though is to always perform a clean install (new installation).
I have done several in-place upgrades without any issues for various of SCOM versions, what I would recommend is to only perform one (1) in-place upgrade, so for example Windows Server 2012 R2 -> Windows Server 2016. If you are performing more than one, for example Windows Server 2012 R2 -> 2016 -> 2019, the risk of corruption or any other issues may get a lot higher, so I would avoid that.
So in the end it will be a decision entirely up to you, but yes an OS in-place upgrade is possible but it may higher the risks of corruption or any other weird side-effects, what you also might need to check is your SQL Server version, that it is also supported.
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