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I don't think there are any automated options for this, although Google Maps is slowly rolling out combined transit & ride share routing in various places and it's already landed in Singapore.
My usual approach is to identify the closest Skytrain/MRT station (preferably on the same road as the destination), go there via train, and then switch to Grab for the last leg. Buses in Bangkok are sufficiently slow and unreliable that I don't use them unless I'm already familiar with the route and its traffic conditions, or I'm in no hurry.