Dear @Lin.Yang2,
Yes, you can linearize an OpenFAST model with ElastoDyn, HydroDyn, and MAP++ enabled.
I’m not exactly sure what platform forces you are looking for; please clarify.
Regarding extraction of the full-system mas matrix through an OpenFAST linearization analysis, see: OpenFast 2nd order Linearization - #2 by Jason.Jonkman
Best regards,