unl0kr 2.0.3
Today I tried to run apt dist-upgrade on my daily driver Byzantium with applied backports and lost luks promt exactly as @JR-Fi reported before. A brief inspection of the problem showed that one of the shared library lost in initrd.img file. To be honestly I’ve wanted to try it for a long time another osk for the boot screen - unl0kr.
unl0kr be built without issues and to replace osk-sdl you just need to fix your /etc/crypttab file (replace osk-sdl-keyscript to unl0kr-keyscript) and rebuild initrd.img file (just run sudo dpkg-reconfigure linux-image-6.6.0-1-librem5). The side effect is that the size of initrd.img reduced down to 26Mb instead of almost 100Mb before (when you remove osk-sdl completely).
Finally, I believe if you replace osk-sdl to unl0kr before the first reboot after applying backports everything must be Ok!