@AFewMistakesAgo you will find a step by step how to here

But you will only see the Downloads folder and folders you have created yourself, not of other apps.

The issue happens to me almost 100% of the time when doing up-down or down-up with the keyboard arrow keys.

I’m not sure whether it ever happens in other cases.

quoting @omz, new beta release 330018, restored the ability to open external folders on ios13

@ccc Done, thanks and sorry, I always try to not forget it, but, my memory is often overloaded 😢