How can I hide an attachment tab/toggle tab in activity

I was able to achieve this using only DOM. To do this - two buttons were created: clicking the first button will trigger the usr.HideButtonRequest request, clicking the second button will trigger the usr.ShowAttachmentsRequest. Here is the code of schema handlers:

handlers: /**SCHEMA_HANDLERS*/[
          {
            request: "usr.HideButtonRequest",
            handler: async (request, next) => {
              let savedAttachmentsElement = document.querySelectorAll('[data-item-marker="Attachments"]')[0];
              request.$context.AttachmentToggleItem = savedAttachmentsElement;
              request.$context.AttachmentToggleItemParentNode = savedAttachmentsElement.parentNode;
              savedAttachmentsElement.parentNode.removeChild(savedAttachmentsElement);
              return next?.handle(request);
            }
          },
          {
            request: "usr.ShowAttachmentsRequest",
            handler: async (request, next) => {
              let attachmentToggleContainer = request.$context.AttachmentToggleItemParentNode;
              let attachmentsToogleItem = request.$context.AttachmentToggleItem;
              attachmentToggleContainer.appendChild(attachmentsToogleItem);
              return next?.handle(request);
            }
          },
        ]/**SCHEMA_HANDLERS*/,

And also two attributes were added to the viewModelConfig property of the schema (in case you don't have it in the schema - create it):

viewModelConfig: {
          attributes: {
            "AttachmentToggleItem": {},
            "AttachmentToggleItemParentNode": {}
          }
        },

As a result the "Attachments" toggle item is removed when the first button is clicked and then displayed when the second button is clicked. What is left to be done is add and test this approach with handlers like HandleViewModelAttributeChangeRequest.