I am sorry for your difficulty. Unfortunately, I don’t know of any of the regulars of this forum who use Notepad++ in Ubuntu.

I don’t see a problem with the Ctrl+TAB selection dialog when on my Win10 machine, so I doubt there is a true bug. You have quite a few tabs open, and it looks like your Ctrl+TAB dialog has a scroll bar – so maybe you have to use that. When I have a large number of tabs open on Win10, if the dialog cannot grow big enough, then if I Ctrl+TAB and keep the Ctrl key pressed, I can use the arrow keys (with Ctrl still pressed) to move through all the files, with it scrolling when I hit the top or bottom. As far as I can tell, that dialog works properly in Windows environment, so I am guessing that the problem you have is with the Ubuntu interpretation of that Windows environment.

In case you didn’t know, Notepad++ is a Windows application, written with the standard Win32 API calls, which don’t directly translate to Linux (Ubuntu or otherwise). I am assuming that the way that Notepad++ is working at all on Ubuntu is that it’s going through Wine or some other translation-layer program which translates the Win32 commands into something that the Linux kernel can understand.

The Notepad++ developers have no control over how Wine (or other similar layers) interprets Win32 calls, and if you were to go to the official issues-reporting page (which isn’t this forum; see the forum’s FAQ section) and report a bug, it would be closed because Ubuntu is not supported by the development team. OTOH, if you can show that Notepad++ has the same problem in a native Win32 environment – ie, in a real Windows OS system – then such a bug report would be more likely to be worked on. (But, as I said above, AFAICT, it’s working as designed and as expected on Windows, so I don’t think there’s a bug on the Notepad++ side.)