Similar to Problems after upgrading Whonix - cannot full size Whonix-Workstation screen
Try to start from command line (terminal emulator) to see more debug output.
stremio: nobody ever asked about this. Unlikely someone here has experience with it.
Try sort out as per https://www.whonix.org/wiki/Free_Support_Principle - meaning try to reproduce this one (minimal) Debian buster (XFCE). See if the same thing happens. If so: use upstream (original developer) support resources to get help.
Alternative: use software available from packages.debian.org. Much easier and much higher chance it would work out of the box.
Also if it must be Stremio, I see a flatpak on their website. Maybe that would work easier.
Simplified: Software from other sources than packages.debian.org… In other words software from other sources than
sudo apt install package-name is often more difficult to install due to dependencies.