I’ve just been trying Shotcut after problems with Kdenlive and I get exactly the same problem. I’m not doing anything complicated, but even something like adding a key frame causes a crash.
I also tried the flatpak version of Shotcut and got the same result.
What is suspicious is that very similar things happen in Kdenlive, though it seems to be using an older version of MLT & Qt. I hadn’t used Kdenlive in months, but last time I did it was fine.
I tried the 21.03.21 AppImage suggested above. When I open the project Shotcut offers to repair it and fails. If I recreate the project, Shotcut seems to work without crashing.
In case it’s relevant this is what I was doing. I’ve taken (wav) audio from a radio program to highlight some points for language learners. I’ve added an abstract video background and one text filter. The crashes seemed to mostly happen when trying to configure the text filter, e.g. adding start/stop points.
Shotcut 21.05.01 (mlt 7, Qt 5.15.3)
Kdenlive 21.04.0 (mlt6, Qt 5.15.2)
Nvidia driver 460.80