Yes, it looks like so far no one has a “direct fix” for the decelerate to stop communication issue between OF Buildbotics controller and PWNCNC Delixi VFD.
So are saying you still have a very long time for spindle to stop, even after using @tjp52 's post processor work-around? It looks like with that work-around you shouldn’t be seeing much more than around 7 seconds of spin-down time.
If it’s still a problem, you’d need post for everyone a little more info, and they could probably get it worked out. At least copies of post processor and/or the last lines of gcode from a program you created. I’m not sure if any of the Delixi VFD settings come into play as well, but it’s worth understanding those related to braking. Good luck!