Hi partner,
This button may not be the original button, but a copy of it, so you can't hide it. You could delete it directly.
For the original button, I can right click and hide it. And, I can't delete it.

For the copied button, I right clicked on it and didn't see Hide. I can delete it.

In my opinion, the original button has been hidden, and the copied button is enabled. You can check it in the HIDE ACTIONS below.
Please refer to this post, the theme is the same as this:
https://community.dynamics.com/365/f/dynamics-365-general-forum/365862/ribbon-button-hide-on-the-subgrid