How do deactivate plymouth boot screen?
Easiest quick fix is to edit the grub line as you boot.
Hold down the shift key so you see the menu. Hit the e key to edit
Edit the 'linux' line, remove the 'quiet' and 'splash'
To disable it in the long run
Edit /etc/default/grub
Change the line – GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash”
to
GRUB_CMDLINE_LINUX_DEFAULT=""
And then update grub
sudo update-grub