Hi anonymous user
you can still monitor those although they are not officially supported.
You can check this thread, where Neha Garg, who is from Microsoft also confirms this.
System Center 2019 - Microsoft Monitoring Agent
Not supported means that they have not (and the will probably will not) tested it, but there aren't any explicit blocks to monitor Windows Server 2008 and R2.
This means - you should be able to still monitor those, but if there are issues with those particular agents, Microsoft will not support you until you upgrade them to a supported OS.
I hope I could clarify this for you!
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Best regards,
Stoyan
Regards,
Stoyan