Unable to rename tabs and controls in my custom ribbon

In Excel for Mac (latest version 16.98), I've created a new tab in the ribbon to put my custom macros in a new group. But I can't change the name of the tab, which remains "New tab", nor the name of the group (which remains "New group"). Nor can I change the name displayed for each macro in the ribbon, or the icon. When I click on the little button with three dots and then "Rename", the new names I type in are not taken into account when I click on "Save".