When using a non-default theme with WindowBlinds on Win 10 (tested builds 2004 (19041.746) and 20H2 (19042.804)), the vertical scrollbar is missing or broken in the application "PuTTY" (or any of the variations of it, such as PuTTY NG or KiTTY). This is an extremely common SSH client. Download: https://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
Depending on the theme, the scrollbar will be completely invisible, or may overlap the right window border or be completely outside the window area (and will be non-functional either way).
I'm using the latest versions of PuTTY and WindowBlinds.
I also tested in a VM with new installs of everything to confirm it wasn't just some other setting on my laptop.
Several themes tested, including "The Captain", "Precision", and "True Classic".
100% monitor scaling, and tested various resolutions including 1920x1080