i've filed a bug report but it seems that it's limited to the desktop manager: with XFCE I had noticed the disappearance of the scroll sliders everywhere in AOO (main window, sidebar, help files, dialogs, ...):
Xubuntu use XFCE. Have you changed the window manager?
I made some tests, (I was mainly waiting for your answer in fact since I know you use Xubuntu) and found out that it was a problem with the themes. Some of the themes have this problem and some don't...
Thanks! I should have tried that earlier.
LibreOffice 25.2 on Linux Mint Debian Edition (LMDE 7 Gigi) and 25.2 portable on Windows 11.
In fact, after checking some old mail from the dev ML, I saw that this had been reported already. I had not used the correct keywords to search the bugzilla (scrollbar is the good one...).
-> Issue 121627 - [GTK] Scrollbars without steppers are buggy
LibreOffice 25.2 on Linux Mint Debian Edition (LMDE 7 Gigi) and 25.2 portable on Windows 11.
There is so little difference between many of the Xubuntu themes (leaving aside the dark and high contrast ones) that after ten minutes I doubt you'd notice you were running Bluebird!
But I hate the blue background for the menus, I prefer the black background for menus. I've found a nice theme: Ambiance light fixed. Have tweaked the base background to have a very light gray instead of white and I'm fine with that.
LibreOffice 25.2 on Linux Mint Debian Edition (LMDE 7 Gigi) and 25.2 portable on Windows 11.