Dear Dhaneesh,
Buckling is not directly considered within OpenFAST. Of course, you can post-process the loads output from OpenFAST to calculate the onset of buckling.
As has been discussed several times on this forum (e.g.: Foundation Stiffness and damping in FAST v8), foundation flexibility and soil-structural interaction are not available in the master branch of OpenFAST. That said, NREL has been working on this recently, by both including a 6x6 stiffness matrix (coupled springs model) at joints in SubDyn and by introducing a new module, SoilDyn. SoilDyn provides an option for a simple 6x6 stiffness matrix, but also includes options for interfacing to the REDWIN DLLs developed by NGI (to model soil-structure interaction via a superelement, including soil hysteresis), as well as and a placeholder for future implementation of a p-y and t-z curves. These are not currently included in a public release, but are being developed in branches on forks of OpenFAST.
Best regards,