The bootsplash actually disappears. But I might have found a reason why this happens. I tried to set up the SBC with Archlinux instead, and noticed that launching kodi-gbm also results in a black screen there; meanwhile, launching kodi-wayland worked, but with half the image cut off, leaving it in an unusable state.
Turns out the lattepanda advertises the onboard screen connector as a display even if there's nothing there. Disabling that display with a kernel parameter fixes kodi-wayland at least, I have not yet tried kodi-gbm again.
The problem is: how do I set the kernel boot params on LibreELEC? I never get a chance to; there is no bootloader screen where I could intercept, nor does the installer offer me to chroot into the fresh installation to make changes before the first boot.