So, this is odd. I installed 4.0.2rc2 and:
1) Changed the template for untrusted: to debian-10. That seemed to work fine.
2) Went to the debian 10 template and installed Blender. That seemed to work fine -- blender will run if I invoke it from the debian-10 template terminal
3) Restarted untrusted: VM. Blender shows up in the available apps in the qubes settings. I move it to selected. It shows up in the menu.
4) Blender does not run when I choose it from the untrusted: menu. Moreover, it will not run from the untrusted: terminal. When I look at /usr/bin in untrusted:, blender is not there (and it still is there in the debian-10 template).