I dont think you can, you should be able to add it back by running that tool again and choosing the Add Show Desktop option. By design, It is not supposed to be removed, that is why there are only 3rd party tools to "hack" the removal of the button.
Thanks for your responce. Even I went through some of the microsoft forms and links also. it seems like what you are telling exactly the same. So we have to use that 3rd party tool only to bring back the "Show Desktop" Icon in the task bar.