I'm here to ensure you can see the category on the Product Categories page.
If the category you're looking for can't be found on the Product Categories page, I recommend clicking the Gear icon at the top of the ACTION column and setting the rows. Some of your categories might be hidden.
If not, I recommend performing some troubleshooting steps to investigate the cause of the issue. You can log in to your QuickBooks Online (QBO) account via incognito mode or a private window. This way, it confirms if the cache is the cause.
Otherwise, switch to a different browser like Firefox, Google Chrome, or Safari. The one you are currently on may be having a temporary issue with QuickBooks, and using a new browser for the moment will allow you to get back to work.