In the past week or so, EndNote 20.5 for Mac (Ventura 13.2.1) stopped enabling superscripts or subscripts to be entered using either the keyboard shortcuts or the drop-down menu. This is VERY ANNOYING for math articles and needs to be fixed soon.
Perhaps you could consider upgrading to the latest version of EndNote, 20.6, which includes enhancements for stability and bug fixes. An upgrade to your macOS Ventura 13.2.1 might also be beneficial as it carries additional bug fixes. Should these updates not alleviate the problem, reaching out to the EndNote support team might prove helpful.
Hope this helps.