I had a similar issue with my laptop after a kernel update, where the keyboard wouldn’t respond on the LUKS screen, but everything else seemed fine. In my case, it turned out to be a kernel bug affecting the USB drivers. I tried rolling back to an older kernel and it worked, just like you’re doing with 6.8.0-49. I’d suggest checking for any new updates for the kernel or the USB drivers. If that doesn’t help, maybe try reinstalling them or looking up specific fixes for your ThinkPad model in the changelogs for that kernel version. Sometimes, newer kernels can cause these compatibility issues until they get patched.