Hi @shankar431 ,
The MOM 2005 Backward Compatibility management pack is used for management packs which were converted from MOM 2005, Microsoft has even some older management packs which have dependencies to this management pack.
This management pack would also give support for MOM 2005 management packs in SCOM 2012, you shouldn't need it anymore in SCOM 2019.
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Best regards,
Leon