Hi @Joseph Patrick ,
For SCOM it doesn't matter whether you use asynchronous or synchronous availability mode, it's mainly up to your organisation's requirements.
I recommend you go through the official Microsoft documentation for designing your SCOM database servers:
SQL Server Design Considerations
https://learn.microsoft.com/en-us/system-center/scom/plan-sqlserver-design?view=sc-om-2019
How to configure Operations Manager to communicate with SQL Server
https://learn.microsoft.com/en-us/system-center/scom/manage-sqlserver-communication?view=sc-om-2019
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Best regards,
Leon