#Install Plymouth
sudo apt-get install plymouth rpd-plym-splash
#ignore errors of non-existing initramfs image, will be created later

#Setup initramfs
#Make initramfs image
sudo update-initramfs -c -k $(uname -r)

#Tell the bootloader to use the generated image. Add to /boot/config.txt:
initramfs initrd.img-X.XX.XX+

#Tell plymouth to use /dev/fb1:
echo "export FRAMEBUFFER=/dev/fb1" | sudo tee /etc/initramfs-tools/conf.d/fb1

#List plymouth themes
plymouth-set-default-theme --list

#Set theme
sudo plymouth-set-default-theme joy

#Update initramfs (add -v to get more info)
sudo update-initramfs -u

Add to /boot/cmdline.txt (all in one line)

fbcon=map:10 splash quiet plymouth.ignore-serial-consoles

Parameter                        | Description
---------------------------------|-----------------------------------------------
fbcon=map:10                     | Console: try /dev/fb1 first, then /dev/fb0
splash                           | Show splash
quiet                            | Don't show boot messages (errors will show)
plymouth.ignore-serial-consoles  |