I’m running out of things to suggest.
No extensions are on in your browser?
Did you try a different browser?
Did you do a fresh reload of the web page? Here reported a similar thing two years ago and it just went away after a few days. That seemed like it might have been a browser issue then and so that is why I suggest trying a hard refresh or another browser.
You should definitely try though using %cd and ls and pwd from in your cells to navigate your filer hierarchy and see what that tells you. If you don’t know what those do, you should look into it. To get you started with that, I’ll share that %cd is the magic version of ‘change directory’ you need to use inside a running Jupyter Notebook to move down your hierarchy. So do %cd <folder name> where the folder is below your working directory that the kernel starts out in.