Thank you for posting in the Community, @therestaurantatw. I'd be happy to provide some information on your question regarding using the tab key to move through QuickBooks Online (QBO).
In the Journal Entry screen, you can press the up arrow to go to the distribution line above or the down arrow to explore the options below. Just a quick heads-up: tab shortcuts work on a per-line basis, so if you need to switch to a different line, you'll have to use your mouse.