To catch all the whistley sibilance you need a de-esser with ~10 bands*, e.g. … Paul-L’s …
(* typical de-essers only have one band).
But even then the reverb in the room is prolonging the sibilance in a way that a typical de-esser won’t touch.
Worth trying a foam cover on the mic, but you may have to apply acoustic treatment to your room to reduce the reverb.