This is a 2.3.0 issue (perhaps older, but unknown to me before).
For myself the upgrade worked perfectly (still on Windows 10 here).
I was helping a user on a different forum setup to be able to use a Teensy 4.1, and after explaining how to place the proper URL in the "Additional boards manager" field I got a response saying he had no such box with a screenshot similar to what I have posted.
I was able to duplicate the problem by resizing my main window smaller, more or less the size you get when you start a new program. In that case, there is part of the box cut off that includes the input box, but there is no visual feedback that that has happened.
The new user is now in business after I explained the fix. But I feel like it may be important to fix this permanently. It appears some of the problem is related to the minimum size of the main window being set to be too small in Y. It does not take a lot of movement above that to get the full dialog to appear.
As an alternative:
The field that has the focus when you open the Preferences dialog box is the OK button.
Use SHIFTTAB twice to get the focus on the field for the additional board managers URLs
Thanks, I will close this. I only reported it because it is not so obvious what is happening to fresh eyes. A small tweak to the minimum size for the main window would make that scroll bar never show up.
