Rock 4C and Plymouth

Is Plymouth for boot splash images for the kernel supported for the Rock 4C, running kernel version 5.10.180. I’ve installed the plymouth-themes and plymouth packages and configured them according to ROCK 4 SE rbuild image not working and adding custom Splash screen - ROCK 4 Series - Radxa Community but I only see a blank screen (on both displays).

When we tested with Plymouth it usually only displays very late for 1-2 seconds, before login manager shows up. The kernel did not initialize the display early enough, and currently we have no solution for this.