I've noticed that with acpi_backlight=vendor, I can't set the screen brightness as low as usual, nor can I adjust it as precisely. With brightnessctl, I can normally set values from 1 to 4882 (maximum brightness), but with the kernel parameter, I'm limited to just 1-15 levels, and level 1 is brighter than the lowest brightness without the kernel parameter. That's too bad.
I'll test it with acpi_backlight=native now. I notice, the brightness range there in brightnessctl is 1-4882.
Hm..it doesn't work. With this kernel parameter the brightness is reset.
So, I'll probably just keep using the default setting without other kernel parameters and add a custom launcher command for the brightness when logging in and suspending the system.