What is your operating system? Windows 10
What is your Shotcut version? 23.06.07 and 23.06.10
Just to let you know that in both of the versions mentioned above (from GitHub), aside from the rectangle control, the Mask: Simple Shape filter doesn’t work.
Hmm… Maybe it is related to my bug report, but I don’t understand how, sorry.
I created that bug report as a result of this bug report. You do not understand Shotcut internals well enough to understand. In any case, I will be pinning the frei0r version that Shotcut’s builds use until that bug is resolved one way or another. Tomorrow’s builds will reflect that temporary fix.