Thanks for keeping in touch with us here in the Community, @esure.
I've got some information about adding a new GL detail account under the expense category in QuickBooks Online (QBO).
For now, the option to add a new Detail Type account is unavailable in QuickBooks Online. However, you can create a sub-account and match it to the closest parent account. To achieve this, please feel free to check out this article: How to create a sub-account in QBO?.
Meanwhile, consider visiting the QuickBooks blog site to get you in the loop about the latest news and what our Product Care Team is working on. This way, you'll know if the feature you want has been added to the current product improvements. Here is a direct link that you can use: https://quickbooks.intuit.com/blog/.
Also, here is a handy help article that you can read through in case you have other QuickBooks concerns, such as managing your inventories, running your reports, setting up payments,etc. to keep track of your business : Help articles content.
Leave a comment below if you've got questions about managing your chart of accounts in QuickBooks Online. I'll be here to give a helping hand. Stay safe and best regards, @esure.