Because of the nature of the problem, I can’t test it without restarting everything so I’ll try to do it later.
The last kernel that works for me is Linux 5.6.0-2-amd64 v5.6.14-1.
With 5.7.something and 5.9.1-1, if I start Anki 2.1.22 (at least if Firefox is running), the image freezes, so that only (Alt+)SysRq+s, (Alt+)SysRq+i and (Alt+)SysRq+b do anything. The +i only kills Xorg; the VC stays frozen.
The video driver is an Intel IGP.
Has anyone had that problem?