I would like the ability to hide an Office Script that I create in one Excel Online file from my other Excel Online files.

And, even more useful: while only scripts created within a file should display by default in that particular file's Script Gallery under the Automate tab, when we select "All My Scripts" (which displays my scripts in the Code Editor pane that opens at the right), it is here that I would like to see all Scripts from all of my Excel files, and from here be able to enable and disable whether a script is available to the workbook I'm in.

Why? Because the list of scripts in the Script Gallery can potentially get congested and confusing if you see all of scripts that you have created in various workbooks. Naming conventions can only do so much, and there is not a lot of name text that displays for each script in the Script Gallery - this means that you have to take the extra time to click All My Scripts to open the Code Editor pane at the right to see the entire list of scripts, and their full names, that have been created in your different workbooks just so that you can find the one script that was written for the file you currently have open.

Per this Office Community reply, current expected behavior is that all Office Scripts that we create (from all of our workbooks) will display in the Script Gallery under the Automate tab for every workbook we author: https://answers.microsoft.com/en-us/msoffice/forum/msofficeexcel-msowin10-mso_o365b/how-to-keep-office-scripts-created-in-excel-online/2a2cc1bc-063a-4a79-b074-23fa970e56c9