Rock 3A quiet splash boot

i am trying to get a clean boot.
I have created a service with systemd that loads me a video at boot, but I cannot eliminate all debug messages at boot, and especially once I start to eliminate the blinking cursor and logging.
In short, I would like that no message would come out on HDMI, black screen, in order to view only my presentation before the desktop.
i tried with some parameters in extlinux.conf
append earlyprintk console = ttyFIQ0,1500000n8 quiet consoleblank = 0 rw init = / sbin / init rootfstype = ext4 rootwait root = UUID = f4dd7250-134a-4fc8-963f-b7137db816d3

But it doesn’t take them into consideration
I don’t know whether to put something in uEnv.txt as well, but I can’t find any documentation on the parameters, it seems that the official Debian Buster tips don’t work here, or have been disabled.

Anyone know how to have a clean boot?

Thanks to anyone

I kind of have an opposite problem with my Rock 4SE, I want to use my own boot screen during boot, but all I have is a black screen for many seconds. The device looks like it was dead for quite a long time, until the Linux log shows up.
I am afraid I cannot help with your problem, but perhaps you (or someone else) knows how to help with mine, meaning: how to replace the default black empty screen with a custom image?
I’m using the latest Radxa Debian image.