Hello there, KW1986.

I've got troubleshooting steps to ensure you'll be able to see the Categories drop-down list when entering credit card charges in QuickBooks Online smoothly.

Excessive cache stored on the regular browser may cause the QuickBooks to have system performance issues. With this, I recommend logging in to your QBO account using a private browser, as it ignores websites from using cache and cookies and doesn’t record any history and data. 

Use these keyboard shortcuts based on the browser you're using:

• For Firefox or Microsoft Edge, press Ctrl + Shift + P.
• For Chrome, press Ctrl + Shift + N.
• For Safari, hold down Command + Shift + N.

If it works in incognito, you'll have to clear the cache of your regular browser. This removes the history or log of sites so you can start with a clean slate. If the steps above don't work, use another supported browser as an alternative.

In case you need steps on how you can manage your transactions in QBO to avoid duplicate data, you can read this article: Categorize online bank transactions in QuickBooks Online.

If you have any additional concerns about entering credit card charges or choosing the right category for the entry, don't hesitate to return to this thread. I want to ensure that everything is taken care of, KW1986. Stay safe.