How to create a local variable of CDT type as array?

Just like any other array. See https://docs.appian.com/suite/help/20.3/Expressions.html#arrays

local!samtask: {
    'type!{urn:com:appian:types}MPPTABSAM_Task'(),
    'type!{urn:com:appian:types}MPPTABSAM_Task'(),
    'type!{urn:com:appian:types}MPPTABSAM_Task'()
}

For a dynamic length you can use foreach() and enumerate() or the repeat() function.

Just like any other array. See https://docs.appian.com/suite/help/20.3/Expressions.html#arrays

local!samtask: {
    'type!{urn:com:appian:types}MPPTABSAM_Task'(),
    'type!{urn:com:appian:types}MPPTABSAM_Task'(),
    'type!{urn:com:appian:types}MPPTABSAM_Task'()
}

For a dynamic length you can use foreach() and enumerate() or the repeat() function.

Thanks