you can however, just that you do programming on your computer instead of neocities' built-in editor. You download the website's files and use notepad++ or visual studio code, then you can drag and drop the modified stuff you made into the website's edit dashboard.
That's probably the only way you can show the updates manually, a packaging sort of method
Same thing has been happening to me when i go to other websites, i dont know whats going on
very weird, first ive come across it, hope it gets worked out soon